The truck is a 1996 4DR 4.3 auto 4WD. After replacing leaking gas lines, a leaking fuel tank, and even a leaking filler neck the truck finally can keep fuel in it! But now there is another problem, I'm wanting to pull my hair out.

The only problem is now that it doesn't want to idle right. It's intermittently too high or too low. After driving a little while at highway speed the engine was idling at about 1200 rpms, it was even pulling me a little bit. Then the idle went down below 500 and wanted to stall. After driving through town for a bit it was fine.

I drove it around a while and the idle is sometimes erratic and it sometimes stumbles right when you hit the throttle and then it runs fine. There are no codes stored or present.

I had access to a scan tool but only for a extremely short time, and the only thing that seemed a little out of place is the TPS voltage would just from .51 to .49 very briefly even when the throttle wasn't touched. A mechanic friend suggested cleaning the throttle plate. I will start with that, but does anybody have other ideas?

Edit: I break one ground strap when redoing the filler neck. It just connected the filler neck to the body, If I remember correctly that strap is just to ground any static electricity when fueling. If that is right it shouldn't affect performance, right?

 

I would definitely suggest cleaning the throttle body. While you are doing that, remove the IAC valve from the side of the throttle body and clean the end of the valve as well as the bore that it goes into. If the IAC valve (IAC = idle air control) is sticking, it can cause an erratic idle.

 

I had a sensor intermittently grounding out causing issues like that. If the tank has been down, there is a chance the FTP sensor wiring has been pinched. That could cause the 5 VDC reference to become erratic. This 5vdc voltage is used by the FTP, TPS, MAP, MAF and EGR sensor also. Talk about a SOB to find!

What are the chances of getting that data tool back to see what else might be acting up when the truck misbehaves?

 

I'll be cleaning the throttle body soon, can the IAC be cleaned with carb clean as well? I seem to remember there been some specific directions for cleaning that thing.

The IAC counts showed fine on the scan tool, but it wasn't acting up at the time so I guess I didn't learn much. I'll be able to use the scan tool again, probably next week. Thanks for the ideas guys.

Edit: I'll check the wiring, but I doubt it's pinched. There is actually quite a bit of room around the tank for wiring.

 

I agree the wiring being pinched would be a "too good to be true" situation, but you have to rule it out.

Catching the live data stream when the truck is acting up is the key to figuring it out.

Follow swartlkk's advice too. I just have some different ideas sometimes.

 

Well, I did a really quick throttle body clean and it didn't act up on a short trip. Not ready to call if fixed yet though. Tomorrow I should have more time to attack the IAC. Hopefully it is something simple after all of the problems the truck has had lately.

 

did you clean the iac yet?

 

Well, I cleaned the IAC, EGR, and the throttle plate again and put some cleaner in the tank. Now it seems fine. Nothing seemed dirty, but something must have worked. It did have a little hesitation one time just after start up but then it was ok. It must have just had some carbon stuck somewhere.