Idles high after being in gear.

[1998_K1500_Sub]

I think for good measure I'm going to change all 3 (what the hell it's only money...lol) And I guess the EGR valve as well. It tests fine but it looks old and who knows what its actually doing.

Eh... you can change them if you like, but I don't like changing things unless I have a reason. One can unknowingly introduce a new problem in the process. Actually, worse than "unknowingly"... one can introduce a problem and then believe there shouldn't be a problem ("It's a new part, that can't be the problem, must be something else"), making the solution to the (new) problem more elusive.

 

[BigRedOne]

Eh... you can change them if you like, but I don't like changing things unless I have a reason. One can unknowingly introduce a new problem in the process. Actually, worse than "unknowingly"... one can introduce a problem and then believe there shouldn't be a problem ("It's a new part, that can't be the problem, must be something else"), making the solution to the (new) problem more elusive.

Agreed! But I am kinda at my wits end. These are the only things left to change and look to be older. Can't hurt. If this don't fix it. It means that its probably a old wiring or grounding issue. That will cost me more money than it's worth to have a professional with patience trace that. My next step is to just junk the whole setup and carb it. Hate to do it but can't waste anymore time or money on this. I've been chasing this for months to no avail. I planned on using this for personal and side gig flipping cheaper cars. So far hasn't made more than 1 trip to do so. If I can't trust it. it's useless to me. Love the truck just can't have this issue hanging over my head.

 

[1998_K1500_Sub]

Agreed! But I am kinda at my wits end. These are the only things left to change and look to be older.

Did I miss it... Have you got the IAC dialed-in yet at idle, like I and others have suggested?

 

[BigRedOne]

Did I miss it... Have you got the IAC dialed-in yet at idle, like I and others have suggested?

Not sure what you mean "dialed in" It idles perfect in park on start up. Once put in gear idle goes high and doesn't come back down till you cycle the key in park. So yes its dialed in in park. The IAC I have(not a screw in. The one with 2 screws to mount) doesn't have a manually adjustable pintle. I've heard of the ones that you can turn and push to close it and that sets it to zero. Mine is not one of those. I can only do the relearn procedure to "set" the pintle base setting. Or am I missing something? If you are refering to setting it by counts on a scan tool. When I had the scan tool hooked up before and had my base idle set to what I was told at the time the counts were 0 at start and moved to 30 which was 750rpms and according to my research this was correct for the 454. I've heard 10 is for the 350. But again once I go into any gear the counts went up to iirc 145 and would fluctuate to 124 and never came back down in gear or park. Cycle the key and back to 30 in park. I believe 145 is completely closed and 0 is completely open. (Open being no air is bleeding by and closed being full air bleed or bypass). Is there another procedure I'm unaware of? I'm still learning this tbi motor.

 

[1998_K1500_Sub]

Ok, different tack:

Has the ECU been examined to see if the MEMCAL is correct?

There’s a four character code on the MEMCAL which should correspond to your engine / powertrain (and a few other factors like emissions, etc).

In the attached example the four character code is ARFP.

Once the code is known one can look up the intended application, as a confirmation.

 

[BigRedOne]

Where do I go to look up what application it is supposed to be associated with? Mine is ANTY and I believe it is for my motor. Again this is going off what other people say not an actual gm lookup site. And can this memcal, Prom, Chip go bad? Could I have a short or corruption that would cause the IAC to act this way? It is a new gm ecu also. Not new memcal. I would buy a new replacement if I new it would cure the issue. Or the 6 pack from Jet that has towing, economy, performance and so on tunes at the touch of a button. But not going to waste the money if its not the problem.

 

[PlayingWithTBI]

I believe 145 is completely closed and 0 is completely open. (Open being no air is bleeding by and closed being full air bleed or bypass)

No, it's the other way around, 0 is closed, 140 is at the open "parked" position.

Mine is ANTY and I believe it is for my motor.

What PCM service number do you have? I'll look it up for you.

 

[1998_K1500_Sub]

Where do I go to look up what application it is supposed to be associated with?

I actually have a database of these MEMCAL codes and their application, but...

Mine is ANTY

Seems like it's likely correct, see here:

7747 ANTY - Help the new guy!

Hi all. I'm new to posting on this forum so have some patience with the new guy :cool: I am writing in hopes someone can help me understand more about the ECU that I recently installed on my 86 GMC K1500 w/ 700R4 transmission. I swapped in a 7.4L from a 92 Suburban and am planning to...

www.gearhead-efi.com

There they say that ANTY was superceded by AZFT. Maybe we can dig around and find out what changed.

can this memcal, Prom, Chip go bad? Could I have a short or corruption that would cause the IAC to act this way?

If it went bad, I doubt it could cause this type of issue, assuming you're not operating in limp-home mode (which it seems you're not).

The ECU seems to be acting as it should otherwise, so I can't imagine this is a case of some sort of error in firmware read from the MEMCAL and executed by the ECU's microprocessor.

It is a new gm ecu also.

Is your replacemnt the "7747" ECU? Please advise.


This IAC behavior is so friggin' odd. The ECU seems (from what I've read here) sane, otherwise.

It appears to me that only the RPM management function of the ECU, a function which employs the IAC, is amiss, which leads me to question...

- is the MEMCAL wrong for this engine / TBI / IAC combination? You need to confirm for us that the ECU is the 7747, but the MEMCAL seems correct

- is the IAC the correct IAC? We went down this road earlier.

- has the MEMCAL been altered? Is there any chance someone's twiddled with the ECU firmware (CHECK: Isn't it a UV-eraseable PROM in the MEMCAL?)

- BigRedOne, was / is your MEMCAL mounted in some sort of carrier, like this (see image attached)? We need to know, if so.

Please read and response.

Meanwhile, I'm still thinking. And I'm still reading that thread I linked, above. There might be insights there and elsewhere.

 

[PlayingWithTBI]

Here's the IAC tables for ANTY - CL Idle = 750 RPM
EDIT: This is with the 1227747 ECM $42 .xdf mask.

You must be registered for see images attach

 

[1998_K1500_Sub]

Did he drive it WITH a scan tool connected?

Has anyone checked that the ECU is receiving / reporting the correct vehicle speed?

My 1995 S10 won't idle-down when in shifted into neutral if the vehicle's in motion; only once the vehicle is stopped (or nearly so) will the ECU return the engine to base idle. So, at least in my case, the vehicle speed bears on the target engine RPM and so IAC.