Idle high, accelerates on it's own.

[thomasstudios]

Having problems. My 98 4x4 Chevy Tahoe has very high idle. Usually around 1000 at start, and after warmup, around 1200. I performed a tuneup w/AC Delco's, new cap/rotor, wires. Changed the IAC valve, (even though I had no codes, and the fuel pump. I am getting a P0304 and a P0507. I hear the K&N hissing really loud vacuuming air into the filter. My Bank 2 fuel trims are around -8 to -17. Bank 1 is fine usually around 0-1. Also once I begin to decelerate, it takes a while while approaching a stoplight. Very hard to stop the truck. Any Ideas? Can this be an O2 sensor? I wish I can afford to take it in or get a live readout. Getting very upset.

[j cAT]

Originally Posted by thomasstudios

Having problems. My 98 4x4 Chevy Tahoe has very high idle. Usually around 1000 at start, and after warmup, around 1200. I performed a tuneup w/AC Delco's, new cap/rotor, wires. Changed the IAC valve, (even though I had no codes, and the fuel pump. I am getting a P0304 and a P0507. I hear the K&N hissing really loud vacuuming air into the filter. My Bank 2 fuel trims are around -8 to -17. Bank 1 is fine usually around 0-1. Also once I begin to decelerate, it takes a while while approaching a stoplight. Very hard to stop the truck. Any Ideas? Can this be an O2 sensor? I wish I can afford to take it in or get a live readout. Getting very upset.

if the air ducting is not secure the maf will not be able to correctly meter the amount of air entering the engine...make sure all ducting is not allowing air to bypass the MAF


when cold the idle should be 1200rpm...then in a shot time drop to about 700rpm...neutral...

the other possibility is the throttle body gasket....

[thomasstudios]

I read the MAF sensor and the wires and it checks good. I even replaced with a known good MAF. Same thing. Still misfire on #4 cylinder, idle does not go down to 700. In fact, it rises to 1200 once warm. Could this be a timing issue with the distributor, o2 sensor maybe? I'm stuck.

[j cAT]

Originally Posted by thomasstudios

I read the MAF sensor and the wires and it checks good. I even replaced with a known good MAF. Same thing. Still misfire on #4 cylinder, idle does not go down to 700. In fact, it rises to 1200 once warm. Could this be a timing issue with the distributor, o2 sensor maybe? I'm stuck.

did I say MAF ??????? air ducting I thought I mentioned must not be any leaks .....to throttle body.....

you also could have an intake manifold leak or bad PCV/hoses etc...anything bypassing the MAF causing the engine to get too much air ..

[thomasstudios]

Originally Posted by j cAT

did I say MAF ??????? air ducting I thought I mentioned must not be any leaks .....to throttle body.....

you also could have an intake manifold leak or bad PCV/hoses etc...anything bypassing the MAF causing the engine to get too much air ..

Thanks. How do I check for leaks on the intake manifold?

[Delusional]

I'm not a mechanic but i've had the same problem in my 96, i changed my intake gasket was good. If i were you id change it because if it goes bad it dumps water into the oil, causing all sorts of other issues.

[thomasstudios]

That sounds like the way to go alright. After doing some research on the same subject, I purchased a can of MAF sensor cleaner and sprayed all of my vacuum lines. I sprayed along the base of the intake and realized that the RPM would rise. I am in the process of tearing this baby up. Thanks a lot. Will let you know how things turn out.

[j cAT]

Originally Posted by thomasstudios

That sounds like the way to go alright. After doing some research on the same subject, I purchased a can of MAF sensor cleaner and sprayed all of my vacuum lines. I sprayed along the base of the intake and realized that the RPM would rise. I am in the process of tearing this baby up. Thanks a lot. Will let you know how things turn out.

what type of coolant do you use ? how often do you service the coolant ?

looks like your on to repairing this..

[thomasstudios]

Originally Posted by j cAT

what type of coolant do you use ? how often do you service the coolant ?

looks like your on to repairing this..

Last time was flushed and refilled by pep boys. I do it once a year. After purchasing the gasket, they told me that this was common and they all tear eventually. Are you driving towards something?

[j cAT]

Originally Posted by thomasstudios

Last time was flushed and refilled by pep boys. I do it once a year. After purchasing the gasket, they told me that this was common and they all tear eventually. Are you driving towards something?

what type of coolant do you use ? did you check that they put the correct amount of coolant to water at least 50%..

pep boys has had a few forum members pissed off..

what I'm getting at is corroded metal usually causes failures of the coolant system....the coolant type and frequency of replacement is for my knowledge...

[thomasstudios]

Originally Posted by j cAT

what type of coolant do you use ? did you check that they put the correct amount of coolant to water at least 50%..

pep boys has had a few forum members pissed off..

what I'm getting at is corroded metal usually causes failures of the coolant system....the coolant type and frequency of replacement is for my knowledge...

It's red, so I'm assuming it's Dex-Cool. I have successfully changed my gaskets on my intake manifold. I went to pep boys just to verify and they add Dex-cool to most cars. Maybe they were lazy and didn't use 50/50 water/coolant. Thanks for the important gouge. I am going to ensure I have 50/50.

[christafer]

One easy quick repair is clean throtle body with old tooth brush and throtle body cleaner...comon for theis tb to get gunk build up and not run right