Hotrodnova66

So I've been chasing this thing for quite some time now. I have an ls2 that was a brand new crate motor, put gmpp wiring harness on it which came with gas pedal and ls7 style maf card. I put headers on it and built a cold air intake for it also. The car never has idled since I first fired it up.

Here is what I know. When the car is cold it will idle (but it takes about 10 seconds to come down after pressing gas pedal) but after it gets up to 200 degrees the car does what it what's. Meaning sometimes it will idle and sometimes it idles around 1500rpm. Tonight I did a test and after 200 degrees the car would come down to idle between 5 seconds being the shortest time and longest being 3 minutes. I'm about 98% sure there is no vacuum leak, I've checked and rechecked again for vacuum leaks.

I pulled the cold air intake off the car had someone in the car with key on and had them lightly press gas pedal and the throttle blade would go backwards for around 10 seconds then come back to "0" which I assume is idle position. Does anyone with dbw have this same thing when lightly pressing gas pedal and throttle body blade going back for some time then returning to 0?

Also I notice at "0" position you can see around 4 sides (maybe 1/16 or so) of the throttle blade but top an bottom are as close as possible to the housing is this normal? When you push the top of the throttle blade backwards the blade is close all around it leaving no gap.

My maf sensor is located 7" away from my 90 degree bend going to the throttle body and 5" after the air filter, mounted in a 4" aluminum pipe. I've read and read placement of this style is critical, do I have it about right or does it need to be moved around?

Sorry for long post but this is driving me crazy. I don't have a computer to read what the motor is doing, so I don't know tps reading but have a buddy coming Saturday with one to plug it in. Just trying to get some input before he comes over

Hotrodnova66

Update to my situation. Had a buddy that works at a GM dealer come over today with his tech 2. Plugged it in the car and everything is showing nothing is wrong with idle except it's idling high. We did a force relearn twice with no effect on the idle. Another page you can set the desired idle, doesn't matter how much you decrease the idle it still idles up but when you put desired idle to its current idle (1300) and go down 25rpm the idle will come down with it to whatever you set but as soon as you hit the pedal it goes back up and doesn't come back down. All the parameters look good as far as the engine running goes.

One funny thing I tried was plugging off the vacuum port that goes from intake to the valley tray and when I did that my map sensor reading went from 20 to 70 and the car would come back down to idle. The hose does not have any leaks either. Thinking its in the tune now that was sent from GM when I purchased the engine controller.

Hotrodnova66

I put a mutlimeter on the gas pedal and one of my signal wires goes to 1.03 volts when the car is idling high. When the car idles normal the signal is showing .98 volts. Also the throttle body blade is going backwards to close when the volts are at 1.03 when at .98 the blade is in the middle of the throttle body. Anyone know what this could mean? Bad gas pedal?

Joe W

I'm not real familiar with drive by wire but if you unhooked the connection to the pedal it should default to idle position ( I assume). Also wondering if you could check volts on the pedal from idle to full throttle with the key on and engine off (of course) If it gives really erratic readings I guess it could be the pedal. I'm having similar issues with my drive by cable on my swap. I actually replaced the throttle body with a spare and the idle got worse.

Hotrodnova66

I got the car warm last night and the idle was high, unplugged the gas pedal and idle returned to normal. Have to shut car off plug the pedal back in and start it back up the idle is high again, unplug it and idle returns to normal. I'm thinking the pedal is wack or there is a problem in the wiring between pedal and throttle body and ECM.

Joe W

Sounds like your getting closer to me! Can you unplug from the throttle body side and check the connections just like you would when checking a throttle position sensor...Check signal, ground, and Volts with a closed throttle then an open throttle. make sure those are in specs. Then have someone work the pedal from closed to open and open to closed and look for a nice gradual change...nothing erratic. If that's fine have a friend move the connections around, including your main connections at your PCM, by hand and look for changes. The rubber seal inside the pcm connections can bind/pinch preventing the pins from making good contact with the PCM. Has your connections been off and back on the PCM?

If all that checks out my guess is it's not the pedal. I'd next check the engine coolant temperature sensor and connection. if this it acting up it could be tricking you pcm into thinking it's running cold. This would change your timing and air/fuel mixtures and cause a high idle.

your idle air control valve may also be at fault and should be checked?

Hope this helps and hope you post back what you find.

Again though, I'm not at all familiar with DBW but these are things I've been doing tracking my issue down. I actually found my ground wire to my TBS not working. I pulled the pin at the PCM and checked continuity from there to my plug and got nothing. I deloomed and unwrapped all tape and found a bad spot in the wire. Totally my fault, as I built the entire harness and somehow missed a wire.This was last night so I don't know if it totally fixed my issue.

Hotrodnova66

I will be checking the wires at throttle body tonight when I get home to make sure everything is good there. I have checked and replaced the coolant temp sensor as I thought it was that but it didn't change anything. I've checked iac values with scanner and everything looks good that I can see, even the o2mv were around 800 (hot and idling normal). This is driving me up the wall trying to figure it out. Hate to take it somewhere and it be something stupid that I overlooked. Good luck with your wire fixing yours. Wish I could find something bad but mine is all brand new, but that doesn't mean anything nowadays.

At this point seems like something is sticking inside my pedal telling the computer to idle up. But the tps sensor (not sure if that reading is from throttle body or pedal) but it showed 10% when the car was idling normal or idling high. But I know the one signal wire from pedal is going up .05 volts when the car is idled up. Seems like I'm getting close but I'm probably going the wrong way.

Joe W

I added mechanical volt, temp and oil gauges to my truck as a safe backup. Here's the thing....My bully dog monitor, plugged into the OBD2, is reading 60 degrees cooler than the mechanical gauge tied into the passenger side head. I would normally assume the mechanical gauge is faulty and trust the pcm reading because there is no temp codes being thrown. But when I turn the engine off the bully dog temp instantly changes to read identical to the mechanical readout (60 degrees higher). So now I'm thinking I have an ECT issue to deal with too. I bring this up because I would have thought nothing was wrong with the ECT....I haven't figured this out yet either??????

Hotrodnova66

I posted in your thread to try something with yours. Mine the temp reading from scanner plugged into the car was the same as my mechanical gauges I have in it.

Joe W

Did you have any luck?

Hotrodnova66

No luck. At this point I don't know what unplugging the pedal means. Because if it's in the pedal I would think it would do it all the time not just when it's hot. So I don't know if it's in the tune, wiring problem or combination of a few things. I have a local tuner in town and probably will just take the car to him and admit defeat on this thing. Hopefully he will be able to figure it out, I've been messing with it for a few months and haven't gotten anywhere.

Joe W

It was interesting when you talked about correcting the issue by plugging off the vacuum line and correcting the problem. I know you have checked many things but was wondering if you checked the MAP sensor/connections. Its one of the main sensors related to load (I know there is others like MAF, TPS but you have probably already checked those).

I hate these puzzles too especially when you put some much time and money into them. Would you mind posting what you find out so I/we can learn from it too?

Joe W

I'm still tracking my issue down and ran across this. Thought it might help

http://easyautodiagnostics.com/gm_el...tle_body_4.php

Have you had any luck?

RedHotG8

iTrader: (1)

If you unplug the gas pedal and the idle returns to normal then the pedal sensor is bad.

Hotrodnova66

I've plugged in the car again with different scanner and I can see pedal pos1 pos2 and commanded pedal pos. 1 is at 19% 2 is at 9% and commanded is at 5%. Talked to a tuner and said its in the tune of the computer. I am taking the car there Friday morning and I'll update when I get back if it was the tune or pedal.

MMWS6

Id be looking at the tune. Check the MAF/MAP and IAT calibrations. You've got a combo of items there that would lead me to believe one, if not all, of those are not set properly in your tune. Did this crate motor come with injectors as well? Need to ensure your injector data is correct in there too or your just tuning around a base problem. I would check it in the following order: Injector Values, IAT Calibration, MAP calibration and then the MAF
A couple of other things can have you running in circles with an LS2 and a LS7 MAF, is there a bend in the intake close to the MAF? Have you installed a Air Straightener(Honeycomb) in front of said MAF? Anyway, an LS7 MAF has a very different value set for measuring IAT's and it has to be changed in a LS2 tune. So go there right after injector values have been verified. As far as the MAP goes, make sure you have the part number in hand for your tuner. They will be able to make sure that the proper values are in there with that info as well. If this is an E40 PCM as I think it is, it is a little bastard child to tune, make sure your tuner has been down the E40 road if it is. The first E40 I tuned kicked my *** for weeks!!!

Hotrodnova66

Took the car today to have it checked out. Tuner said everything looked right in the tune and didn't see anything that should make the car idle as high as it's doing. I have the e38? ECM I believe in the car, came with the gmpp controller set up I bought to run the motor. The motor was a brand new ls2 crate motor came with injectors and everything already on the motor. Tuner said to bring car back next week as he was really busy today and he will throw it on the dyno and see if anything jumps out on there. So back to square one for now.

Hotrodnova66

The maf is at least 9 inches away from my 90 degree bend going to the throttle body. Have no honey comb in front of the maf sensor, but I do know if the maf is loose and you move it up and down in the intake pipe you can make the car idle down but if you leave the maf there and press throttle it will go back up and have to move sensor around again for it to idle. At this point I'm frustrated haha

RedHotG8

iTrader: (1)

Sounds like you need to mount the MAF more securely. That's obviously the problem since it determines airflow to the motor which regulates the amount of fuel flow and the idle speed.

Hotrodnova66

The maf sensor is mounted securely but I was saying if you remove the two bolts holding it in and move it up and down it will make the car idle sometimes.