High idle issue 98 350

[Smitty82]

Trying to figure out why and what the problem is. It only idles high went I place in neutral to cruise to a stop sign. Also I tacks like I have auto cruise control at 30mph in 3rd gear. Any help thanks!

 

[michael hurd]

Vacuum leak.

 

[Smitty82]

Vacuum leak.

Wouldn't it idel high all the time if it was a vacuum leak

 

[Smitty82]

Once I come to a dead stand still the truck idles down to 650~ like it should. I can rev up and it goes back down. This issue only happens going down the road at around 25-40 mph

 

[michael hurd]

Not sure of that issue.

 

[Smitty82]

Not sure of that issue.

It does this cold or hot......

 

[Smitty82]

Auto zone guy said maybe cam sensor or tps just looking for a better answer be for I got and just start buying parts!

 

[Chevy1500]

I had a throttle position sensor go bad on mine and it caused a pretty similar issue to what you are seeing.
I tracked it down using a scan tool, it said I was at 60% throttle when I was really only at about 15%. Pulled it off and it was all corroded inside. 10 minutes later I had a new one on and it ran like a champ.
I had spent every bit of a week or more trying to track the issue down because it happened at the same time I put my new motor and 0411 pcm in the truck.

Kyle

 

[Smitty82]

I had a throttle position sensor go bad on mine and it caused a pretty similar issue to what you are seeing.
I tracked it down using a scan tool, it said I was at 60% throttle when I was really only at about 15%. Pulled it off and it was all corroded inside. 10 minutes later I had a new one on and it ran like a champ.
I had spent every bit of a week or more trying to track the issue down because it happened at the same time I put my new motor and 0411 pcm in the truck.

Kyle

Thanks im gonna get one after work. I also just see on you tube that the Idle air control valve may be bad....

 

[Chevy1500]

If you have access to a decent scan tool, it will show the live information on both the TPS and the IAC.
The GM Tech II definitely shows it and I think some of the more advanced consumer scan tools will too. Maybe even the loaners from your local auto store.
I don't remember what the IAC should read under normal conditions but if you cant find it on google, I can get that info or somebody else could probably chime in with it.

Kyle