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Ive been dealing with an eratic idle and just changed out my IAC valve only to make my issue worse. When in gear sitting at a stop light i can feel the truck pull against my brakes with and a rise in RPM on and off. In reverse its even more noticeable. If anyone has any idea or experienced the same problem im all ears. Ive researched and searched my ass off between here and FSB and im at a loss... Im going to change out my TPS (throttle position sensor) maybe that is going bad and telling the truck to idle up?? Any help is appreciated.

Ryan I had a similar issue when I lost my EGR...also check for vacuum leaks I have seen leaky lines also cause this issue. IRC there is a resistance check for the TPS to tell you if its bad but I may be way off there.

I'd do a code scan before touching anything. That way you will know where to start and save headaches and money.

Jeremy,thanks for the comment ive chcked all the vaccum lines and im good there. The tps issue im not aware of...
Rod,ive got my scan gauge hooked up all the time and the only code ive thrown was the IAC whcich ive sinced changed. Nothing else since then.

You may try disconnecting the battery to reset the computer...IRC 96 had a computer that "Learns" So it may be adjusting other than that I would check the EGR it may be sticking as I said I had the same thing happen just before it failed and then threw the code haha...

I would check the refrence voltage at the iac and make sure the tps is where its supposed to be. I've also heard the pcmcia could have some faults and cause this. Not too many things.will make the engine rev higher on its own.

I've got the same issue Ryan. Replaced the EGR, TPS, IAC, checked vaccuum, cleared codes, etc. Ended up removing the IAC and adjusting the idle normally. I've been running like that for the last 3 years or so with no noticeable ill effects. Certainly not the proper fix, but it will keep you driveable while you research the problem.

Poor connection at the grounding location could cause this too but which ground I'm unsure. I would remove and clean them if needed. The grounding on these vehicles.is fairly redundant so it would seem to me unlikely but still a possibility.

yikes wrote:I've got the same issue Ryan. Replaced the EGR, TPS, IAC, checked vaccuum, cleared codes, etc. Ended up removing the IAC and adjusting the idle normally. I've been running like that for the last 3 years or so with no noticeable ill effects. Certainly not the proper fix, but it will keep you driveable while you research the problem.

Im going to check the voltage at the TPS and go from there. Did you just unplug the IAC? How do you manually set the idle?

Ok so the tps voltage checks out fine. I decided to disconnect the iac and go for a drive, ides smooth no surging or anything weird. Never threw a code with it disconnected either... maybe i just got a shitty iac from the parts store?? Im going to run it as is for awhile and see what happens. Thanks for the help fellas.

RyanDS650X wrote:Ok so the tps voltage checks out fine. I decided to disconnect the iac and go for a drive, ides smooth no surging or anything weird. Never threw a code with it disconnected either... maybe i just got a shitty iac from the parts store?? Im going to run it as is for awhile and see what happens. Thanks for the help fellas.

My IAC took a shit in baja so I manually adjusted the throttle screw. No code after that.

Replaced IAC in states and backed throttle screw all the way out and good as new. Pull it off and make sure the thing moves freely. My original one was seized and no amount of carb cleaner or muscling was moving it...probably had to do with lots of silt and only a couple filter changes while prerunning.

I've gotten bad IAC's from the parts store before. If the ground bad on the IAC circut it could cause the refrence voltage to jump around and cause your symptom. I would probe the wires and check the refrence voltage as well as the voltage drop across the sensor. Likely you gave a faulty IAC

Well im at a loss at this point and could use some help.
Ive replace the IAC (again), TPS, all new gaskets on upper and lower intakes as well as throttle body, there are NO vacuum leaks.

Idle will randomly go up too 1400rpm and stay there. No more surging but with the brakes on and truck stopped i can feel it pulling against the brakes. Ive noticed that the speedo needle jumps whenever the idle acts up also.
I disconnected the VSS and the idle goes to normal but i cant drive like that cuz the trans goes into limp mode.

I pull the grey plug out of the timing modual and the idle goes to normal also. With the grey plug back in it shooting the timing with a gun its at 10* but then jumps to 20* when it idles up. Seems like it thinks it under load when its not...

help?

How do i manually adjust the throttle screw?

Sounds like a faulty tps. Do not adjust the throttle screw if it was never tampered with.

Tps is brand new and the voltage sweep is within range, so was the one i replaced it with... .8v at idle to 3.5v all the way open

How long did you run it for?

Did you replace the vss. Funny that it idles back down when you disconnect it.

No i havnt. Im going to call about it tomorrow.

I followed the reset protocol Randy. Idle for 15 minutes while the idle hunts then went for a drive. Came back to the shop put it in park and same high idle with bouncing speedo.