strange high idle... AGAIN!

[paxton350]

ok i thought i got to the root of this problem before a few months ago but apparently not... i havnt driven my z too much since i did a spec 3 clutch and steel flywheel install, 1.6 rockers, electric waterpump, msd 6a box, egr and air pump delete, complete hvac deletion and pcm4less tuning to comp for everything... i took her out today for a drive and opened it up on the highway up to about 4500rpm in 5th and then shifted into neutral however the idle didnt fall back to 1k.... it stopped and stayed at about 3500rpm and could NOT get it to fall again until i shut the car off for about 20 min... on my supercharger intake elbow i have a HKS BOV which last time i had this problem i took the BOV off and secured some aluminum foil between the elbow and the bov deleting the BOV thinking it was letting unmetered air into the inatake manifold... i was wrong, the problem is back agian and its such a pain! im thinking would the problem lie in the clutch/flywheel? a vacuum leak? egr block off plates? pcmforless tuning? unadjusted rockers? ALSO the car is throwing NO codes which is making this more frustrating... thanks for any insight.....

-chris

[paxton350]

one other thing ive noticed last night is that i can actually tap the gas and rev the motor a bit while the idle seems to be "sticking" at a high level (2500-3500rpm) then the idle drops back to normal (around 1000rpm) but i have to tap the gas, kinda weird.... any thoughts?

[4THGEN Z]

No expert here but maybe TPS? Actual throttle cable/linkage sticking?

[paxton350]

well the spring on the throttlebody is well lubed and not corroted really, doesnt seem like its sticking although how would i tell for sure? i mean i can depress the pedal fully and the butterfly will open then close completely... if it was a tps sensor woulnt the pcm throw a code?

[paxton350]

any other ideas? clutch break in possibly? MAF going south? (maf is descreened)?

[Kevin - Blown 95 TA]

I have a second spring on mine. The BBK 58 had the bellcrank welded when new and no play in it, but it would stick a little bit when the plastic cover was on. Couldn't see any place it was rubbing, and fooled around with it for a while, then added a seecond spring (which is a damn good idea anyway in case the first one ever breaks) and problem solved.

During my rebuild, I lost that second spring and forgot aout it and the problem was back. Put a spring back on there, and back to normal.

[paxton350]

thanks kevin that makes sense... esp how i tap the pedal and it stops sticking... however where and how would i rig up that second spring? i have a holley t.b like the one below.....

[Kevin - Blown 95 TA]

I hooked one end to the bellcrank and the other end to a small hole I drilled in the bracket right behind it that's bolted to the intake - the one that holds the TB cover on. If I get out to the garage later I'll take a pic of it, ut it's pretty simple. Just find a way to attach it to th upper part of the bellcrank and to something behind it so that it works through the entire range of travel.

[paxton350]

what kind of spring did you use? home depot item or? im probably going to just drill a hole on that brass throttle lever (bellcrank right?) and rig a spring to the bracket... id appreciate that picture kevin id like to see how you did that exactly... thanks!

[Kevin - Blown 95 TA]

Here it is, something you might be able to find in any hardware store. I have an extra connection on the bellcrank that made it easy, you might have to improvise. actually, in looking at the picture, I might have originally had it in the little hole near the top, but seems to work OK where it's at. I'll have to look at that later...

[fastTa]

You said you had a recent mail order tune which means you had the PCM without power for a while. Whenever the PCM loses power, the control module's learned position of the IAC valve pintle is lost. To re-establish the valve pintle position baseline, do the following:

1. Press on loud pedal to at least 1/4 of the way down, or 25% TPS
2. Start the motor, once it fires let go of the loud pedal, then allow the motor to run for at least 5 seconds
3. Turn ignition "OFF" for 10 seconds
4. Restart motor

The best thing to do is to get it on a scanner and narrow down the possibilities. It could very well be a problem with the throttle cable and/or linkage, but it could also be PCM or electrically oriented as well. High idles can stem from a number of different tables....RPM vs. TPS, RPM vs. Coolant Temp, Throttle Follower IAC Offset vs. MPH, etc., etc., etc.. Best thing to do would be to log a bunch of cold starts and see what is going on. You'll be able to look at your IAC counts and TPS voltage and compare the two as well.

The IAC reset procedure can be effective some of the time, but you might also try the Idle Learn Procedure.

This is straight out of my 1998 Alldata. Keep in mind it is assuming that you have just re-installed the PCM after getting it back:

Automatic Transmission:

1 Turn off the ignition

2 Restore the PCM battery feed

3 Turn Off the AC controls

4 Set the parking brake and block the drive wheels

5 Start the engine

6 Allow the engine coolant temperature to reach 158°F (70°C)

7 Shift the transmission selector into the drive range

8 Allow the engine to idle for 5 minutes

9 Turn on the AC controls

10 Allow the engine to idle for 5 minutes

11 Shift the transmission selector into Park

12 Allow the engine to idle for 5 minutes

13 Turn off the AC controls

14 Allow the engine to idle for 5 minutes

15 Turn off the engine for 15 seconds



Manual Transmission:

1 Turn Off the ignition

2 Restore the PCM battery feed

3 Turn Off the AC controls

4 Set the parking brake and block the drive wheels

5 Transmission in neutral

6 Start the engine

7 Allow the engine coolant temperature to reach 158°F (70°C)

8 Turn on the AC controls

9 Allow the engine to idle for 5 minutes

10 Turn off the AC controls

11 Allow the engine to idle for 5 minutes

12 Turn off the engine for 15 seconds

[4THGEN Z]

Hey keRm...didn't you have to rig up a secondary spring like Kevin for the Holley on your Comp?

[paxton350]

hey thanks for that pic kevin im definately going to rig up that secondary spring probably next weekend... fastta when i start her up next im definately going to try that idle relearn and IAC reset procedure as well i was quite unaware of that... thanks everyone for the help!