new GN guy needs idle help


New Member
New to the dark side, i need some help PLEASE!!!!! I have a 87 GN with 39,000 miles on it. It is 100% stock and I can't get it to idle. The car sat for about 5 years without regular driving. When I got the car I changed the fuel filter and plug wires and it idled fine.

In the past month it started idleing rough. I bought a scanmaster and have adjusted the tps to .42. The best WOT number I can get 4.30. I have set it from .40 to .46 and still the best WOT is 4.30. The car idles rough but runs very good through about 3/4 throttle. It actually pulls harder at 3/4 throttle than WOT, I assume it is from the tps and the ecm not seeing it as WOT???

I was able to adjust the IAC to get a reading of 25 before adjusting the tps. Once I set the tps, the iac reading went up to ?? (out of normal range and I didn't write it down). I adjusted the IAC back down and then the tps reading went out of whack. I decied to adjust the tps correctly and now I get a IPC reading of 00 or 01.

I have found NO vacuum leaks anywhere.

Here are the other numbers:
af 06, l8 45, int 128, BL 150, ats 57, iac 01, cc 218, mal 22 and 44

If my little brain understands some of this, it appears that the maf is ok, the ecm is adding fuel (long-term) to compensate for something?????

Is this as easy as a bad tps? I don't want to just start changing parts until I have someone with experience look at this too. Any help would be greatly appreciated.

Also, how do I post stuff in my profile? Thx.
You need to pull the TPS forward when setting it. If is settles back on it's mount, you can see 4.30+, but the throttle blade is not open all the way.

It seems you have done some research on what you need, (as far as number go) and that is great!

You may want to check the resistance on the coil to see if it is getting ready to crap out. even with 4.30 you should get good even power through the throttle. Just not all it's got.
ok, i loosened the tps and shoved it as far toward the firewall as I could. I set it to .42 and still only got 4.30 wot. I started the car and had a reading of 06 for the iac. I adjusted the screw clockwise (turning it out against the throttle linkage) and the maximum I could get was 12. I let it idle for a few minutes and it went to 00 again. The car had sat for about 45 minutes between tests. any other help would be appreciated... it is driving me nuts.
A reading of 4.30 volts on the TPS at WOT is more than enough and has nothing to do with your idle problem. First thing I would do is change the O2 sensor and get an updated chip from Eric (TurboTweak) :)
idle wild

Look for a cracked drivers side manifold also pull up on the EGR valve and make sure its seated and not stuck. Pull your FLOOR mat out from under the gas pedal. Now check your TPS. Hope this helps..;)
Don't let the TPS/IAC setting mess with you..... starting with the TPS adjusted properly..... adjust the throttle screw (engine at operating temp.... in park)... adjusting the throttle screw to open the throttle blade will tend to lower the IAC number... and adjusting the screw to close the throttle blade will raise the IAC number. Once you get the IAC adjusted properly... then re-adjust the TPS. Worst case you have to make one more adjustment to each..... but usually it only takes one adjustment of each.

I agree with others... a BLM of 150 is a little high... and need some attention....throttle body gasket leak? vacuum line leak? EGR leak? Intake gasket leak? Any fresh air that enters the engine without going thru the maf meter... is unmetered air... and the ECU will have to add fuel to compensate... hence the high BLM's. IMHO... usually high BLM's are caused by some sort of un-metered air entering the intake tract....

Thanks for all the great ideas. I am traveling for work and won't be able to mess with it until later the week or weekend. I will be sure to check again for vacuum leaks, check the egr valve, and plan to replace the o2 sensor, if need be. I will post again later this week as to what I have found.
If i read the SM number correctly you have 2 malfunction faults may wanna fix those first go to to get the break down of the fault number and start their 44 maybe a bad o2 sensor
Years ago....

Following advice in one of Razor's posts, I made a gasket for the vacuum block which blocked all vacuum distribution, and my BLM went from 150 to 128-129. I had a vacuum leak somewhere, it was just a matter of finding it. With a BLM of 150, you have a vacuum leak. :)

Do a search on vacuum leaks or high BLM, look for Razor's treatise about it. :cool:

You should be sure to have fresh vacuum lines everywhere.
Might sound crazy, but make sure the cap is on the turbo inlet where the pipe going to the passenger side valve cover used to be. Mine fell off, drove me nuts trying to find the leak. Also, to clarify what Lee said, he removed the distribution block on top of the throttle body, placed a gasket (with no holes in it) over the hole, and replaced the vacuum block. If your blm's drop to 128, then you know one of those darn hoses is causing your leak, or the leak is at the vacuum block itself. A smoke test might also help find it, or GBody Parts sells a kit that attaches to the turbo that you pump up with air, to help find it. Good luck. I think I once had a bad O ring on a fuel injector that was leaking. You can press in the injectors with your fingers while the car is running. If idle changes, there is your leak. You can also spray everthing with soapy water and look for bubbles.
Ok, here's what I have done now that I am home again. 1) checked for leaks yet again. 2) replaced the o2 sensor. 3) pulled on the egr valve and it immediately sucked back down and appeared to seat again (no change in ilde). 4) not related to the problems changed the plugs and wires. Readjusted the tps and iac (now ..42 and 35). Still have mal codes 22 and 44. BL still in the 150 range. It is also idling at about 1150 rpm. WHat is normal for these cars?

There is one thing that I can not figure what it is. I have inserted a picture in hopes it may be a part of the issue. However, when i plug it there is no change in the idle. It is on the passenger side valve cover.
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As far as other leaks throttle body, etc. leaks. I went back through every maintenance record and verified that the engine has never been apart. Can the TB gasket go bad without ever being broken down?

Again, any help would be appreciated. On another note... I LOVE THIS CAR. I wish I would have bought one years ago.
Bad pic. but it looks like the boost solenoid on the pass. side valve cover if that's what it is it's supposed to be like that is normal. Also where are you located one of these guys local to you maybe able to help
Is that a red tenticle'd octopuss?

J/K.... I'd say the wastegate solenoid as well..... if hooked up might notive the boost higher by a lb or two vs unhooking and plugging off the vacuum line that goes to it....
You need to clear the trouble codes and drive it around some. The ECM stores the trouble codes even after the problems are repaired. Does the check engine light still come on?

The high BLM and the high idle tells me that there is definitely some sort of vacuum leak.

Take out the floor mat as someone stated before. They sometimes prevent you from depressing the gas pedal fully. Have someone press the gas pedal to the floor and you look into the throttle body to make sure that you are getting WOT.