coryforsenate

iTrader: (1)

Hi, so I'm having a high idle issue. So I replaced the idle air control valve, cleaned the throttle body all over and inside. Got a lot better. But it still does a high idle about 1 in 5 drives, when before it was like 4 in 5 drives. The high idle isn't as high as it was when the IAC valve was malfunctioning. And sometimes when take my foot off the gas at low speeds the rpm's will remain slightly higher than normal, resulting the vehicle maintaining higher speeds than it should with no gas.

Should I be looking for a vacuum leak? If it's likely a vacuum leak, why wouldn't it occur most/every time?

Could it be an egr issue? The egr was recently replaced per a code and failure of cleaning to fix it, but I forgot to clean out the "pipe" that leads to and from it.

RPM WS6

iTrader: (3)

Has the idle been high enough for long enough to give you a P0507 code?

When the high idle occurs, does it ever go away on its own? If not, can you immediately clear the condition with a quick restart of the engine, or does it need to cool down completely and restart from cold to idle properly?

What tends to trigger the condition? Use of the A/C, extended driving at a higher speeds, idling for long periods? Or is it totally random?

Do you have a comprehensive OBD scanner to look at certain data when the issue occurs (such as IAC values, TPS voltage/percentage, fuel trims)?

Has the car done this for as long as you've owned it, or is this a new condition? If the latter, did it develop after any sort of recent repairs or changes?

Any modifications, and/or custom tuning?

coryforsenate

iTrader: (1)

I've never gotten a P0507 code. I'll occasionally get a P1406, EGR position more than 10% off expected position. I tried cleaning the valve, didn't fix it, so I replaced the EGR valve. I still will get a P1406, but it's much rarer.

My vehicle's manufacturer idle says it's should be about 600-700 rpm. But what I'm seeing is around 1,100-1,500. It will sometimes go away on it's own and idle at normal rpm's.

It's completely random, as far as I can tell. Sometimes it'll idle normally, then start doing high rpm's. Sometimes it'll start out with higher rpm's, then it'll start idling normally. Sometimes it'll do the high rpm's the entire trip and sometimes idle normally the whole trip.

I can have scanner than can read some values, like TPS but it's in terms of % rather than voltage. Some values are in normal values like you'd get with a high endscanner.

No mods or custom tuning. I'd say it started doing it about a year ago but over time has gone from being ignorable to a regularly recurring issue.

When I replaced the EGR valve, I did not clean the bore. I was wondering if the bore has narrowed a lot from carbon buildup, if it can cause my problems. I was thinking to try running a brass bore brush through it and turning the engine on with the valve off to blow out at carbon debris.

coryforsenate

iTrader: (1)

Oh, in addition to the EGR valve, the IAC valve and the TPS were also replaced recently.

coryforsenate

iTrader: (1)

For instance, just now while I was driving. Without putting my foot on the gas, I was going just over 20mph. Also got another P1406 code. It was misbehaving before the code but it got worse after the code showed up.

Oh, and this is really rare but sometimes when it's idling at the proper 600-700 rpm it'll drop down to around 500 rpm and the engine will, for only a split second, sound like it's stalling before immediately going back up to proper idle speeds. This is really rare, only 2-3 times a month but some more info to try to diagnose the problem.

coryforsenate

iTrader: (1)

I found this thread on GM vehicles with a lot of different people having the same problem, high idle and vehicle accelerating without pushing the gas.
https://www.gminsidenews.com/forums/...41/index2.html

Suggested fixes were replacing the TPS, EGR, IAC, throttle body gasket, MAF, and fuel pressure regulator due to failed diaphragm. I've replaced all of these except the throttle body gasket and fuel pressure regulator. Of course, there's no guarantee the new part wasn't defective. I replaced the TPS multiple times due to a TPS code with OEM ACDelco ones and they were all bad out of the box but the Wells TPS seemed to work fine (no codes for two months so far).

I'm going to see if it does it again when I drive home and hook up my semi-decent scanner to get some numerical readings and report back.

coryforsenate

iTrader: (1)

One guy said he solved the issue by driving around with the EGR unplugged until the CEL came on, turning the engine off, then plugging it back in and driving around until the code went away. I guess that's one way to do the zero position EGR reset?

coryforsenate

iTrader: (1)

Okay, here's some data

Started it up and in park the numbers are (it's behaving):

revs ~700 rpm
vacuum 22in/Hg
TPS bounces between 0 and 2.5%
intake 3.6 psi
MAF 6 g/s

When I started driving the problem started, high rpm's and accelerating even when my foot isn't on the gas. These numbers are when my foot is NOT on the gas

revs 1000-1500 rpm
vacuum 18.5in/Hg
TPS bounces 0 and 5%
intake 5 psi
MAF 12g/s

I wish my scanner would give the TPS in voltage, especially since it gives everything else in raw data. But that's a no-go.

coryforsenate

iTrader: (1)

Drove a few miles with the EGR unplugged, got an immediate P1406. Didn't clear it. When I got home I turned it off and plugged the EGR back in. Will see what happens tomorrow.

RPM WS6

iTrader: (3)

The TPS value should not be bouncing between 0-2.5 or 0-5.0% while sitting at idle with your foot off the gas, nor should the percentages be that high at any time during idle. That's the main indicator I see as an issue so far, and it sounds like you've had some issues with getting various TPS sensors to work properly. I wonder if there is an issue with the harness somewhere - I seem to recall another member having issues with inconsistent TPS values and some similar problems as a result, but I don't remember who or what thread it was in. Those OEM sensors which were giving you codes....perhaps they were more sensitive to whatever related issue is happening, and the aftermarket one might be less precise with delivering a MIL but still impacted by the same problem.

FYI.... even 700rpm is too high of an idle speed in P/N if the engine is fully warmed up and the tuning is 100% stock. The factory idle speed for all A4 LS1 F-bodies from 1998-'02 is 550rpm in gear, 650rpm in P/N at operating temp.

You didn't mention IAC values. If actual idle speed is higher than commanded idle speed, then IAC counts should be at or near 0 (which would be the PCM's attempt to get idle speed back under control). If idle speed is higher than commanded but IAC counts are higher than 0, then something could be amiss with the data that the PCM is receiving (and those elevated TPS readings definitely don't look right.)

coryforsenate

iTrader: (1)

I did splice in a new pigtail that connects to the TPS but I haven't tried tracing the wires back to the PCM. I had always wondered about the fluctuation in TPS values but didn't know if there was a degree of error that's normal before it rises to the level that it suggests a problem. My throttle body is clean as a whistle and very firm.Throttle cable seems fine also.

I had a lot of issues with the ACDelco OEM TPS's. Actually went through 6 of them before I tried a different brand. It would drive horribly with them. The aftermarket sensor, driving still has some issues but with the ACDelco ones I would get really harsh shifts and the rpm issue was much worse.

My scanner doesn't give IAC values. Do you have a recommendation for an inexpensive scanner that can give all the raw data? What I listed above is the limit of raw data that my scanner collects. There's a few other values, like coolant temp, speed, etc, that I don't think are relevant to this issue.

RPM WS6

iTrader: (3)

That TPS fluctuation should not be happening, I've never seen that with any of mine. I think I do recall sometimes seeing the value settle at something like 0.4% at idle (rather than 0.0%) but never any higher than that, and never any continual fluctuation across such a large range (meaning never up to 2.5 or 5% like you're seeing.)

It's crazy that 6 different OEM sensors would be bad right out of the box. Unless there is a recent quality issue with the GM replacements, I would suspect something else to be at the root of this issue (i.e. odds are very low of getting so many bad ones in a row).

As for a scanner, I'm still using an old AutoTap program on a 20 year old laptop. It's ancient, but still works just fine for gathering this type of comprehensive data. Getting a look at IAC values would help establish whether or not the PCM is making an effort to correct the idle speed (my guess however, based on those elevated TPS readings, is that it is not).

coryforsenate

iTrader: (1)

Is the connector for the AutoTap program an OBDII to USB connector? Actually, if it's from 20 years ago it wouldn't have USB...

I'm on the website right now for the program and they're pretty scant on the physical components of this system and Googling around doesn't turn up a whole lot of stuff on connecting the OBDII to a computer. This idle issue has been driving me crazy. It's more frustrating than when I rebuilt my 4l60E. I'm at work right now so I'll look into how I can get some IAC values without spending a grand on a super scanner later.

I was thinking it's possible the OEM sensors were a bad batch issue, since the only reason I had 6 of them was because Amazon accidentally sent me one box of six sensors instead of just one sensor. All from the same lot number. I don't remember where these were made but I know some of the OEM stuff is now made in China.

I just got in my brass bore brushes and will do some scrubbing of the EGR bore. It's never been cleaned in all 23 years of its life and I do rarely get a P1406 despite replacing the EGR. The instances of P1406 dropped dramatically after replacing the EGR.


Let's say the I get the IAC values and it suggests the PCM is not making an effort to correct the idle speed, what would be the next step?

And I appreciate you taking the time to help me figure this out, RPM WS6.

RPM WS6

iTrader: (3)

I bought all that equipment many years ago, I think I got the A-Tap program in 2000. It's OBDII to serial port, not USB. I'm not even sure what type of offerings they have at this point, most folks end up buying a complete tuning suite rather than just comprehensive scanning software. No such thing existed when I got AutoTap, not even LS1 Edit was on the market yet.

I definitely understand the frustration of these driveability issues which seem impossible to solve. I've had some similar ones regarding idle problems, but not directly comparable to yours as my symptoms and data readings were a bit different.

If the PCM is not commanding the IAC shut, then your high idle condition is likely stemming from the PCM commanding the IAC open more than it should (likely in accordance with the elevated TPS readings). So, you'd have to figure out why you're seeing those elevated (2.5-5%) and fluctuating TPS values at idle (perhaps a harness or lingering connector issue?)

If IAC values are at or near 0, then the PCM recognizes that the idle speed is too high and it's trying to lower it by reducing idle air flow (which often also comes with a P0507 code). This would suggest that air is entering somewhere which it shouldn't be, and that the PCM is trying, but unable, to correct for such. But I think this is less likely, since you are in fact seeing some erroneous TPS readings.

On all of my A4 LS1 F-bodies, IAC values (when stock) can fall in the range of 10-25 (A/C off) depending on P/N vs. in gear, how hot the engine is, and how long it has been idling. But within that range, the most typical readings are usually in the area of 14-22 at full operating temp.

coryforsenate

iTrader: (1)

Instead of buying a more powerful scanner, can I measure the voltage to/from the IAC and determine the information that way?

RPM WS6

iTrader: (3)

I imagine you could, but I have no idea how those voltage values would translate (IAC voltage is not something I've ever looked at, nor does my software support this as a parameter).

I'm not sure that it's critical to invest in better scanning equipment just to get IAC values at this point though, as those IAC values are probably going to confirm that the PCM is not trying to correct the condition (likely due to bad data from the TPS, e.g. those 2.5-5% readings when it should be 0% or at least under 1%, something is wrong with those TPS values and that's likely the root of the issue - the question is, why are they reading higher than they should?) This theory is further supported by the fact that you're not seeing a P0507 even when the idle speed is double what it should be.

coryforsenate

iTrader: (1)

May I ask what I should check next? Again, I really appreciate you taking the time to guide me.

I've replaced the TPS multiple times, with two different brands, to no avail and the throttle isn't loose at all. So I'm not feeling that it's likely so many TPS's are bad in a row.

I know one of the coolant temp sensors is on one of the same wires as the TPS, per the electrical diagram. I don't remember which wire specifically but if there was an issue with the sensor or the temp sensor's wire could it cause the readings from the TPS to be unstable? I've never had any issues that would make me question that the temperature readout is wrong, going by what the gauge on the dash says.

I've been keeping a log of rpm behavior and something I noticed today was that when I park the rpm's went up to 1,500, held for about 3 seconds, then dropped to about 900 for about 3 seconds, then shot back up to 1,500 for about 3 seconds, then dropped. This behavior repeated a few times before I shut off the engine. Would that suggest the IAC/PCM are attempting to cope with the erratic TPS signal?

RPM WS6

iTrader: (3)

Have you tried following the diagnostic matrix in the factory service manual for the TPS codes that you were getting when you used the GM sensors? I guess I would start there, as this seems to be an issue rooted in those false TPS readings (since you are certain that the throttle blade is properly closed when it reads 2.5-5% and fluctuates...and I'm assuming that nobody has ever adjusted the throttle blade idle position further open than stock - and even if they did, it shouldn't be fluctuating). This could be due to a wiring/connector issue, or perhaps some internal PCM fault leading to the IAC being commanded open further than it should based on misinterpreted TPS data. But there should be a diagnostic process for those DTCs in the service manual which might point you towards some possible answers.

If you don't have the factory service manual set and don't want to buy them, you might be able to find a link online. I've seen a few over the years, but I don't have a link handy at the moment.

You also might just try an online search of the DTCs themselves, see what sort of successful repairs other folks have found when getting those codes (perhaps leading you towards something you haven't tried or inspected yet). Obviously, you've already tried many different TPS sensors so the codes (and issue) might be caused by some other component in the circuit (wiring, connector, PCM itself, etc.)

coryforsenate

iTrader: (1)

Good lord, those factory service manuals are expensive. But I see I can buy a one week subscription for $10.

Quick question, if it was a PCM issue could flashing it possibly fix it? I never had TPS issues until I replaced the factory one when I was an a preventative maintenance kick and ever since then I've had problems, with them getting noticeably worse this past year. I ask this because I found this about older vehicles and newer parts and I keep getting a P1406 even though I replaced the EGR valve with an ACDelco OEM one and they say the solution for their case was to flash the PCM.

"For example, on certain GM vehicles the Check Engine light comes on and sets a code P1406 that indicates a fault in the position of the exhaust gas recirculation (EGR) valve. Cleaning or replacing the EGR valve and clearing the code does not fix the vehicle because the code usually returns. The real problem is the OBD II programming in the PCM. When the PCM commands the EGR valve to open to check its operation, it isn't allowing enough time for the valve to respond. A brand new valve takes only about 50 milliseconds to open but an older valve may take up to 350 milliseconds or longer - which is not long enough to cause a real NOx emissions failure but is long enough to trip a fault code. The fix in this instance is to reflash the PCM with new instructions that allow more time for the EGR valve to respond."

The TPS code when I would get it was either P0120 or P0122. I can always swap one of the old sensors to get it to make the code again to be certain.

RPM WS6

iTrader: (3)

So this issue began right after you replaced the original TPS....and, if I'm understanding correctly, there was nothing actually wrong with the original TPS, you just replaced it for the sake of general maintenance? I just want to be sure I understand this part. No PCM tuning should be needed in this case, since the problem did not arise from a modification, nor would you want the PCM to accept fuzzy/faulty or "slow" readings from the TPS.

So, and again assuming that I understand your above post correctly, the obvious thing would be to try that original sensor again, since it used to work fine. But I'm assuming you've probably already done this at some point and it didn't solve the issue. I also recall you mentioning earlier that you replaced the connector - there may be something amiss with this repair or the replacement connector itself. Have you tried jiggling the wires/connector while the engine is running to see if anything happens to the idle speed (and/or if there are any changes in TPS readings on your scanner)?

Also, have you ever tried a basic TPS reset procedure? This is usually necessary to get it to read 0% again after mechanically adjusting the throttle blade, but perhaps it might help in your case as well. It's a simple thing, here's a link:

https://ls1tech.com/forums/pcm-diagn...learn-tps.html

And here is one of the threads I mentioned earlier, about other members having a similar problem as yours. You may find this one helpful as it seems the OP of this thread also replaced his connector and ended up having to redo the wiring on this to solve the problem. So you may in fact still have a wiring related issue with that connector, and fixing that (and going with one of those GM sensors) might be the final repair in your case:

https://ls1tech.com/forums/general-m...connector.html