For the last 70k miles, my car has had a problem with reving by itself to 1.5k, 2.0k, 3.0k, sometime even to 3500 RPM. Currently I have the Crane Cams power tuner tune on my car. The problem manifests under these conditions:

-Amount of rev related to speed of car, greater than 30mph provides the highest rpm increase (2-3k)
-Car returns to normal idle at stop after 1-2 seconds
-Revs are most noticable when the car is not in gear, but when it is in gear the speed of the car remains pretty constant, even with my foot off the gas (ie, the car does not engine brake)
-Pushing the clutch in (even in neutral) brings the RPMs down from 2-3K to 1500 rpm.

What I have done to try to solve the problem and the result:

-Checked for leaks in the intake system(none found)
-Replaced PCV with oriface style PCV(no effect)
-Replaced all PCV piping and fittings(no effect)
-Replaced intake seals(no effect)
-Took it to a tuner with EFI Live and other diagnostic tools. He was able to set the throttle cracker to 1500 be he remarked that this is not normal, and it was reset to the settings beforehand.
-Made hole in throttle body blade smaller (rougher start-up, fixed the rev-up problem for about 3 minutes, then it was back to reving, but not as high, ~2k rpms)
-Adjusted idle throttle body blade position screw (rougher start up, held the rev-ups to about 1500 most of the time, but eventually rpms started climbing into the 2ks.)

What options I have to do next:
-New throttle body
-New TPS, IAC, and other sensors

I am 99% sure this is a tuning issue since all the physical ways of adjusting this have lead to the computer adjusting to rev the engine up. I am absolutely stumped at this point. Anyone with similar issues?

 

very similiar and i posted about it but like you nobody has helped me with my problem either.....so good luck

 

Thanks for the bump...

Someone asked if I have leaky vacuum hoses - Ive check them many times. I cannot find a leak.

 

... I gotta think you have a leak somewhere. Hard for it to be a tuning thing... it needs air to rev up. So long as the iac is good that's about all it controls at idle. On second thought, I can't understand from your post of your problem is at idle or not. Check the hose between the PCv valve and the throttle. Also you can replace the brake booster check valve... pump the brakes and see if that revs you engine. ...just a few ideas fwiw

 

Check IAC counts at hot idle. I bet they are at zero. Get them into the 40-65ish range at hot idle. You need to close the blade to get the count to come up. Make sure that TPS reports 0% at 0% as well. Once that is set if the issue persists, it's time to look at airflow in the tune.

 

Thanks for the help.

The problem is only when the car is in motion, and the gearbox is in nuetral and the clutch is not pushed in. The reving is directly related to two conditions: Speed of the vehicle, and sensor on the clutch engaugement.


Ive replaced my entire PCV system with a fixed oriface type, and I am sure there are no leaks. When I pump the brakes, there is no change to engine idle.


My throttle body has been "ported" but ive tried covering up the hole in the blade and adjusting the idle screw, but it will still rev to 2k under the conditions I posted above. I will be procuring a new throttle body shortly.

 

I KNOW the issue is when the car is in motion, you already said that. You still have to do what I said to get to the bottom of this.

 

I will have to take my car back to the tuner to get that info, but I will take care of it and see if we can work it out.

 

Sorry to have sounded short; I generally make the assumption that if someone is posting here in tuning over a specific issue, they have the ability to work on their own calibration.

If there is no vacuum leak, your TB has to be setup at warm idle and then idle airflow logging and tuning have to be done. No competent tuner would need to be told any of this though.

 

Thanks everyone for the help so far. I have tried two solutions thus far:

Trial Solution 1: Screwed with (literally, adjusted the screw and hole size) for my current modified ported throttle body. I was able to keep the engine from reving up about 70% of the time. Instead the engine would go from 600 rpm back to 800 rpm and cycled like this until I came to a stop. 30% of the time it would rev up to 2000-2500 and hold there.

Trial Solution 2: New, stock, non-molested throttle body installed. Had to install the oil pressure sensor as well, so I took the entire system apart, checked for leaks (again) and finding none I put it back together with the new stock throttle body and stock blade hole size. I reset the TPS and left the IAC unplugged while the TPS reset.

This seem to solve the problem, and I couldnt have been more happy. The RPMs were coming down in a predictable and quick fashion, RPM would hang at 1500 for about 1.5 seconds then come down to 800-1000, regardless of the speed. Perfect! I couldn't be happier.

Something happened after the test drive. Its like the computer said and the problem started up again. It continues to hang at 2000-3000 rpm until I come to a complete stop. I havent had the time to take it to the tuner to check the IAC count, but that will be as soon as possible, hopefully, this week. Help me get this gremlin out of my car!!!

 

When you swapped throttle bodies did you take the IAC from the original and move it to the new one or did the new one come with an IAC and TPS attached? My IAC went out and gave me a similar but intermittent problem, however it did show a code. I didn't mess with it, I replaced the IAC that day and haven't had a problem since.

 

Same sensors as the old one. I havent been getting any codes. Might try an IAC swap with my brother's car (00 SS) and see how she does.

 

Tried the IAC swap, no dice. I am taking it to the tuner Tomorrow. He is suggesting it is uncommanded airflow.

 

my car is ironically doing basically the exact same thing you described, above 45 mph in neutral it will stay about 1800-2k but once i slow down under that the idle drops to normal

 

Problem solved! Doc at EFI Alchemy in Green Cove Springs, FL helped me figure it out.

With the car at idle, he measured the IAC counts. 110 was too high. With the car off, we adjusted the throttle screw, unpluged the TPS sensor, turned key on and waited for the code, key off, key on, cleared error code, and started it up to see what the IAC count was. Once we were in the 40-60 range, we took it out for a test run. The issue was still happening at this point. Doc tweeked the throttle cracker and throttle follower from the stock settings. He was able to adjust these to have the car idle at 1300 rpm while in motion, and 900 while at a stop. While I have been driving it, I've noticed it vary between 700-1600 rpm while in motion. For the most part she stays around 1300.

I was only able to obtain these results by fixing all the physical issues with the car: the throttle body was drilled and the port job was letting in plenty of air. I replaced it with a stock throttle body. My crankcase ventilation system was completely replaced, as it had plenty of holes in it. Throttle body and intake gaskets where replaced and properly torqued.