I drove my car to my shop to paint my hood and after I painted it, it died while in reverse just backing it out of the booth. It would run really rough and the RPM's would drop and it would die. I tried to start it a few more times. One of those times I tried to keep the rpm's up to keep it from dying and it seemed to not register the gas pedal. Then the next few times it did register and I revved it and put it in gear to move it out of the way and it died again. I started it a few more times and it seemed like it would stay running in park for longer, but when I put it in drive or reverse it would drop the rpms and die, though I believe it did die in par a few times. Scanned it and got no codes. I had it towed to my house and when it got there it wouldn't die, it ran fine going into my driveway and I left it on and put it in gear a few times, and it stayed running, but it did seem like it would idle high, sometmes the tb gets stuck in park and if you rev it or physically push it down at the tb end it would return to normal neutral idle, but it wouldn't, it would idle at like 1200-1400.

Last week a rocker came loose and I had it towed home again and I re-adjusted the rockers to 3/4 turn and put polylocks on this time. These are stock rockers btw. Seemed I finally got it right. Then when I went to leave to go somewhere I accidentally hit an aftermarket security override button with my foot and it blew a fusible link. I repaired the fusible link and everything went fine until now.

The motor has roughly 15,000 miles on it and ever since I blew a headgasket about 6 months ago it's been nothing but trouble. I also replaced the fuel pump when i ran it dry and also the opti during the headgasket repair because there was a parts store opti on there and I didn't like it. It has a madZ28 tune as of abut 3/11/09 Coil is new, ICM has been recently tested, FPR and EGR are new. I am leaning towards something like TPS or IAC...what do you think?

 

Sounds like an intermittent problem with the IAC motor. There are no codes for the IAC. If you check it with a scanner, it will just tell you what the PCM is trying to set the IAC position to, not whether the IAC is actually working. But the scanner will show if the PCM is trying to control the high and low idle problems by altering the IAC "counts". That might confirm a problem with the IAC.

 

Someone on another forum suggested that the paint vapors still in the booth (they do stay in there a while) caused the car to run rich and over time the car leaned itself out to normal with fresh air. I suppose it could be possible, but I will probably check the IAC and get a new one just in case.

 

engine off the Idle air mtr pos is about 37 steps, engine on it takes about 2-3 seconds to get to 56/57 and doesn't fluctuate. I did this before and after I took out the IAC and cleaned it, and the hole it goes in.

 

And it stays at that position while its idling at 1200-1400RPM?

 

sorry, it idles normal now about 750 in drive, 950-1000 in park, and has been since after I took it home. And yes it is steady. Actually I don't think I remembered that correctly, in park it goes up from 31 to 37, THEN it goes to 56/57 in drive.

 

What did madz28 set the idle at, in park and in neutral?

What is your coolant temp sensor reading on the scanner? If the temp is significantly lower than actual, the PCM may be elevating the idle per the table of temp vs RPM.

What is your TPS sensor reading closed throttle? If the voltage is greater than 1.0 the PCM may elevate the idle. Ditto with a VSS that isn't reading "0".

 

I asked for a 700 idle, I don't believe there was an option for idle or neutral, just desired idle. It idles at about 725 according to the scanner in drive, when I initially put it into drive it dips into 625-650 for a moment and stabilizes about 700.

Temp sensor seems normal, both temp sensors are new, replaced 6 months ago. It reads 70* when I first star it and climbs from there, after running in the driveway it went up to about 170*.

TPS is at .66, but I did notice the sensor has a broken clip in it where it holds the pigtail connector.

IAC in open loop is higher in drive than in closed loop - like 110 steps in drive. It slowly goes down to near 40-52 as it warms up, while in park it is at 35-37, nearly matching the "learned idle position" which fluctuates between 33-35, but mostly stays still. VSS stays at 0.

Is it normal that sometimes when putting it from park to drive or reverse, that my headlights and dome lights dim?

bought a new IAC and TPS along with a complete new vacuum line set a lot of the lines to the TB and around it are kind of thrown together and mickey moused, so it couldn't hurt. I've also always been concerned about my descreened MAF, done by a previous owner....do you think it's worth it to get a new screened one just to limit problems in the future, or is it not that big of a deal?

 

It's never worth it to remove the screen. There is never any measurable gain but there can be idle problems a plenty when it's gone. The problem is going to be getting one. It appears from the parts lookup that GM doesn't give the screen a part number. So finding one could be a hassle.

I'm also concerned about the fact that you have a CAI and a 54 mm TB with a stock MAF.

 

You can't replace just the screen, you need to get the whole thing, that's the real problem. And I thought aftermarket MAFs were junk? Most heavily modified people use the stock one.....or I thought?

 

Any MAF other than stock, especially in my application shouldn't be needed and would be unreliable.

I feel like I'm just aimlessly throwing parts at it, and If I ever decide to drive it to work again as my DD it will just happen again and I won't know why.

 

Not sure I understand what the problem is.... but it appears that now everything is running normally. And it appears you had some evidence of the TP blades sticking? Are you no longer having any knid of problem with the idle speed? The IAC numbers you posted look normal.

 

I guess so, it's just in my mind if I can't find it, I feel unsafe and am afraid it will just happen again, only in the worst/dangerous circumstance. it would appear that it fixed itself, but when does that ever happen? I guess I just can't believe it.

I've been testing and taking short drives every night since and have found no problems and no abnormal operational data that I could see from my scanner. I will be replacing the IAC anyhow, and the TPS for the broken clip anyhow, along with the vac lines for extra security. Now do I match the new IAC length to the old one if it is longer? Can I just push it on or does it twist or what?

 

http://shbox.com/1/4th_gen_tech2.html#iac_reset

 

Yea, I read that, but am not sure how to move it, I guess I'll just see when it comes in the mail today. Thanks again for all your help, injuneer, you're always johnny on the spot on these tech threads. Now I just hope it doesn't come back....