3.2 surging, completely random, 124 set in in mem

[Huntervf]

I'm still having probs with my 95 ATX, here's a quick review:

Won't idle when cold and/or ambient temp is below 60 degrees. It acts like the engine isn't going through it's cold startup procedures because even when it's warm it idles a little low and it never idles "up" at startup.

That's not my main concern at the moment though...I mentioned it in case someone can draw a coorelation to it. Since removing/cleaning the intake a couple weeks ago I've had a problem with the engine surging sporadically. Sometimes it will just rev up to about 1600-1800 RPM's all on it's own, then drop back to anywhere between 500 & 1000. It doesn't bounce up and down...it's like someone is pressing on the gas, holds it for a few seconds then lets off. It will do this while driving or when parked. It seems to go in cycles...it will do it quite a lot (say for 5-10 minutes) then it will be fine and not act up at all. I occasionally get a CE light, the only code being set to memory is 124: TP voltage was higher than expected (fuel systems). I'm assuming this refers to the throttle position sensor but I replaced it and my shop told me they couldn't adjust it, and it was still surging before I replaced the TPS.

I'm also getting codes 411 & 412 during KOER, which says idle speed system not controlling idle properly (idle too high for 411 & too low for 412). Yeah, that's pretty much what's wrong shrug

I was still having a surging problem before replacing the TPS...when I ordered the part the shop told me there were two different types, perhaps I have the wrong one?

Incidently, in the past two weeks here's what I've done:

Removed/disassembled and thoroughly cleaned the intake & IAB ports.
Replaced upper intake manifold gaskets
Cleaned throttle body
Cleaned MAF & swapped MAF's with no change
Replaced IAB
Replaced 02 sensors
Cleared computer & reset idle SEVERAL times


Anyone have some input on this for me? I'm very suspicious that my computer is bad due to the no cold idle condition & the fact that I cannot run a goose test, but the surging only started after I put the intake back together so I'm not sure it's related. I've triple checked everything I did, the question is what did I forget?

 

[luigisho]

I don't have the manual procedures for the 3 digit codes. Have you followed the steps for all the codes produced so far?

You know a few SHO people in the area. If your computer is suspect, a working swap would let you know for sure.

 

[Mike Kopstain]

Chris, since the problems timing is in occurence with the removal of the intake, I think you are looking at a vacuum leak.

 

[Huntervf]

Would a vaccum leak be sporadic though? I thought of that as well...I can't hear anything out of the ordinary and all my inspections thus far haven't found anything shrug

What kind of timetable am I looking at to swap a computer on an ATX? When I had my parts car I remember it being a PITA to get the computer out, and I don't want to tie up or damage anyone else's car just to try and troubleshoot mine. Anyone have a spare computer lying around?

 

[Mr Anonymous]

Code 124 often has more to due with low EGR flow than an actual bad TPS. For reference, the TPS you got should say CX-1426 on the box. (FWIW, there are several codes like this where simply replacing the sensor isn't the first step to take (if at all), 124 is one of those codes...)

I agree with Mike that you are probably looking at a vacuum leak, and yes, vacuum leaks can be intermittent too. IIWM, I'd remove and disassemble the intake again, replacing all of the intake gaskets, and carefully inspecting the runner-to-head gaskets and replacing them if there's any coating missing where the runners attach to the heads. I'd also want to closely inspect the intake manifold hoses to make sure they are not rigid/checked/brittle. Finally, I'd be sure to root the IAB and EGR passages, as well as making sure the air passage from the TB to the IAB is clear as well.

You could also try testing for a vacuum leak -- searching under 'vacuum leak' should bring up a couple of methods for doing so. Also, double check the vacuum connections to the EGR valve and DPFE sensor.

 

[luigisho]

Vacuum leak sounds like a good place to start. To swap the computer you lower the glove out of the way, detach the small plastic bracket supporting the rear of the processor and unscrew the bolt in the middle of the wiring plug on the engine side of the firewall. Should take 5 min. 10 if something is giving you a hard time.

 

[Sho-N-Go]

Hey chris I had one just like this a couple years ago. The rubber connector rolled over on me and yes caused a intermittant leak. I do agree it is a vaccuum leak on the Idle surges. Check the IAB plate is on right with the right gasket in the right place it does make a difference.

Chuck

 

[Huntervf]

Ok...here's an update:

It looks like a minute vaccum leak was indeed the culprit. The car still has cold idling issues and I'm attending to that now, but the surging seems to be taken care of. This past weekend I removed the intake and replaced the EGR gasket, lower intake gaskets and both IAB gaskets. The IAB and intake gaskets seemed ok, the intake gaskets did have some of the black paint peeling off and there were a couple spots that MAY have not been seated well. The EGR gasket however was toast...it nearly broke in two when I first took it off, I had applied a little bit of RTV when I reinstalled it figuring that it would be ok. I can't say for certain where the problem was but after replacing all the gaskets, double checking all my intake assemblies & gaskets (I had replaced all the intake manifold gaskets the first time around) the surging condition has not come back and in fact the car idles better overall now, but it still will not idle on it's own when cold...I have a computer on the way so we'll see what happens when I install it.

I am however still getting a CE light from time to time and it still sets a code 124: TP voltage was/is higher than expected. Now shortly after I got the car I put a couple turns on the idle set screw (you know, the one they say not to turn ) to help the car idle up a bit better until I figured out the cold idle problem. Would the fact that the TB sits open just a little bit more trigger the code?

But hey, THANKS for your help! No idle at cold is one thing, but when the car just takes off on it's own it's a little disconcerting! I'll keep everyone posted on the new 'puter & cold idle situation thumb

 

[Slo-Sho]

Get a DMM and test the middle wire at the TPS and verify .95 volts w/ the ignition in the run position.

 

[sdpatt]

Changing the position of the hard idle stop screw was a bad thing to do. You really need to return the set scew to its original position. You need to reset the base idle speed to 850 rpm with the SPOUT connector and IAB valve disconnected. A strobe should be used to measure the engine speed since the tachomoeter is not calibrated. Then reset the TPS idle voltage to less than 1.0V. The surging idle was probably due to a vacuum leak in the EGR system. You seem to have created your own problems.

 

[Huntervf]

No no no...the no idle condition when cold was a pre existing problem when I bought the car. And I can't reset the idle when it won't idle...after much trouble shooting I feel pretty confident that a new computer is in order. In short it seems like the car simply isn't "idling up" at startup, like it's not getting the command to do so. When it's warm it does ok but even then it doesn't idle up at all. When it's cold it needs help for a couple minutes before it will hold an idle and then it only holds 500-600 rpm. The only codes I get are the 124 in memory and KOER 411 and 412, idle speed too high and idle speed to low...and that doesn't tell me anything aside from what I already know. I've gone over most every sensor I can think of, replaced the IAB & cleaned the intake VERY well (hence the surging prob I had...I guess the EGR gasket was worse than I thought.) There seems to be no other problem other than the car isn't getting the signal to idle up at startup. Also, when I first ran codes the car would not run the KOER test correctly, even after numerous attempts. The next day I tried again and it ran the test ok, but now it won't run a cylinder balance test.

So a new 'puter is on it's way...in the meantime the couple turns I put on the idle screw makes the car drivable without much trouble...now it will idle on it's own after only a minute or so, before it would take 10-15 minutes.

 

[projectSHO89]

deleted - duplicate

Steve

<small>[ May 14, 2003, 10:23 PM: Message edited by: projectSHO89 ]</small>

 

[projectSHO89]

Actually, the PCED includes the procedure for properly adjusting the setscrew.

Here is the synopsis from the 92 service CD for the 3.0L SHO on whether the adjustment is needed:

1> Engine off. Disc neg batt cable for a min of 5 minutes, then reconnect

2> Start engine and stabilize it for two minutes, then goose engine and let it return to idle, lightly depress and release the throttle and let engine idle. Does engine idle properly? Note: if fan comes on, wait for it to shut off.

3> If engine does not idle properly, proceed with procedure per the PCED.

Steve

 

[AutoSHO]

In regard to the cold idle problem, have you replaced the ECT sensor? That would cause no idle when cold...

 

[Huntervf]

I have not replaced the ECT...that was one of my first thoughts but the ECT is functioning 100%.