IACV troubleshooting questions

[msggunny]

I posted this on another board and i decided to use the "shotgun" approach to see what kind of responses i get. Thanks in advance.

The issue with my IACV has gotten worse. It now kills the engine when i idle the engine while its moving, even a little bit. See below for a better explanation.

I unplugged the IACV and it is doing almost the same thing, almost like the computer isn't "sensing" the IACV. The only change was that after i unplugged it, the truck wouldn't die out when i idled it while it was moving.

This leads me to believe that there is another issue besides the ones i am looking at, namely the VSS. The IACV will do its "check" when i have it out of the manifold and plugged in, the plunger will go out and then back in to set the idle position.

Any ideas as to why it would run the same with it disconnected as it does when its connected?

Anyone know of anyone in the NE area that can reset a ECU's adaptive values? I would send it out and drive the series but i dont have a heater in it and its snowed in....

Thanks

Quick historical update of the issue from an older post:

97 D1 5 speed 102k miles.

New IACV so it shouldn't be that.

I am having a hard time figuring this one out (not really hard since i'm dumb)

After the engine is warmed up and she is has been run a bit the idle will do weird things when i go to neutral, either by putting the clutch in or pulling the shifter out of gear.

It falls to normal idle rpm, bumps around and then drops to almost nothing, some times reading 0 rpm on the tach but my scan gauge rpm reads 300 - 400 rpm does this a few times and then settles down to normal idle rpm.

batt light and sometimes the oil light comes on because of the low rpm.

Its the worst when i coast into a stop.

if i down shift as much as possible until i come to a stop it seems to make it recover faster but still falls on its face a bit.

After it recovers it idles fine, i have tried revving the engine at a stop and it goes to normal idle just fine.

I am inclined to suspect it may have something to do with the VSS. Again, it only does it when the vehicle is moving and not at a stop.

it did something similar in Virginia this summer, part of the issue was a bad IACV and i replaced it and just replaced that one a month ago.

My VSS appears to be working fine, although when i first got it 30K ago it would do the "drop to 0mph while your driving" and "act like you hit the electronic governor at speed" things but appeared to fix its self (which is bull **** i am sure)

Any input would be appreciated, I dont want to just thrown a VSS at it and keep my fingers crossed.

Thanks.

[Les Parker]

Hello there,

Have you checked the vacuum lines from the servo to inlet manifold and the vacuum line to the charcoal canister?
I found that on my 97 5 speed by "jiggling" these 2 lines the revvs would vary from 2k to 200 RPM.
They are now resealed and all is well.

[msggunny]

Hello there,

Have you checked the vacuum lines from the servo to inlet manifold and the vacuum line to the charcoal canister?
I found that on my 97 5 speed by "jiggling" these 2 lines the revvs would vary from 2k to 200 RPM.
They are now resealed and all is well.

I checked them yesterday, thanks though.

I also changed out the VSS yesterday, no joy....

[Les Parker]

What do you mean by the "VSS" ?

Have you checked the fuel pressure?

Mine would also stall out, especially when in slow moving traffic.

Put a new fuel pump in and all has been well for the last 20k

[msggunny]

What do you mean by the "VSS" ?

Have you checked the fuel pressure?

Mine would also stall out, especially when in slow moving traffic.

Put a new fuel pump in and all has been well for the last 20k

VSS: vehicle speed sensor

I checked the pressure when it was first starting up, no issues good pressure. I may have to check it again though.

[luckyjoe]

I have similar issues, but still suspect a vacuum leak. It's quite erratic, and not possible to duplicate. I've recently pointed at the cruise control vacuum pump, and isolated it from system. The idle has been at 700rpm for two days now, ? ! We'll see when it surfaces again.

I did notice one overlooked hose, behind the plenum, connected to a dashpot-looking thing. I bet that hose it factory original, since it's so hard to reach. I plan to replace it tomorrow.

You're not alone Gunny...

[msggunny]

Just to update those who may be following this.

I decided to unplug the VSS all together and run it using my GPS for speed.

It idles just fine now, no issues.

Either the new genuine VSS is as bad as the one i replaced it with or the ECU is having an issue reading what the VSS is telling it.

I am going to go with the ECU issue.

It should be fine until i can get the SIII back on the road and the ECU sent somewhere to get checked and repaired.

Thanks for the input.
Richard

[luckyjoe]

Msggunny,

Did I read elsewhere that you resolved your issue with a new MAF?

After yet another wild google search I found a posting were they started with the MAF unplugged and the issue was resolved. Replaced the MAF and all was well.

So, I unplugged the MAF, started, ran, and held idle after fully warmed up! Should I get a new MAF?????

[msggunny]

Msggunny,

Did I read elsewhere that you resolved your issue with a new MAF?

After yet another wild google search I found a posting were they started with the MAF unplugged and the issue was resolved. Replaced the MAF and all was well.

So, I unplugged the MAF, started, ran, and held idle after fully warmed up! Should I get a new MAF?????

You did, it was my MAF. I cleaned the one I had and it runs fine now. Yours may need more than a cleaning, but I would start there.

Get MAF cleaner, apparently brake cleaner can damage the plastic housing.