I got a 95 gmc pickup 5.7 when i start it it idles at 1400 rpms for a few seconds then it drops down to 1000 rpms which i think its still to high but when its in gear it idles at 800 rpms just replaced the egr valve and check for vacuum leaks and its all good need help figuring it out, any ideas would help thank you.

 

Thats not too far off. I would try to find a scanner to plug in that reads live data and compare the ECM's reading to the gauge. Sometimes the gauge can be off a little. If that coresponds with the gauge then I would double check vacuum leaks, and then check the IAC valve. If the throttle body hasn't been off in a while I would pull it and replace the gasket between it and the intake (known to leak) and give the throttle body a thorough cleaning. Especially in the IAC chamber. The auto parts stores have an all in one rebuild kit for these throttle bodies and they can make a big difference.

 

cool ill go ahead and check that, but i just replaced the iac valve a few minutes ago i started it up and idled about 1200 or 1300 rpms but in the instructions it says to drive it on a 40mph road for the iac valve to adjust it self but haven't really tried it yet, but thanks for the info bro

 

Did you clean the port that the IAC screws into? They are known to get carboned up and cause issues. You can look down from the top of the TB and see where it goes in to get an idea if it is nasty in there.

 

no i did not ill probably clean it tomorrow but i did run it with the new iac valve and a new throttle position sensor and it idles a little under 1000rpms runs better too but when it idles a little under 1000 rpms the check engine light comes on but when i put in gear and idles down to 800 rpms the light turns off or if i rev it a little it goes off but over all it does run a little bit better and check engine light is off when im driving i just cant get it to idle right but i will clean the iac port, do you think a new speed control sensor might help too or any other sensor what do you think .

 

I wouldn't keep throwing sensors at it - that gets expensive. These motor are fairly simple and a high idle is usually a vacuum leak. If the throttle body to intake is leaking it can be hard to do the spray test depending on where the gasket has failed. Have you checked your timing (another freebie)? I would try to do all the free checks first before throwing any more money at it. You have to unplug the advance wire to check the timing and it should be at zero or slightly advanced. Alot of them I have seen come in retarded and the customer is amazed at how just a few degree adjustment will make their truck run and idle. Personally I would buy the TB rebuild kit unless you are sure it was done recently. With those miles it has to be due. Put the whole kit in it, it not only will familiarize you with how it works, but you want to use everything you just paid for. I say that b/c more times than not people are afraid to go too deep into it and just replace the easy gaskets. With that installed double & triple check your vacuum lines (don't forget about the MAP sensor that plugs into the back of the TB) and then check the timing. If all that looks good I would then get a couple vacuum caps and start plugging off the individual ports on the TB one at a time to see if that changes the idle. If one makes it idle better than you know you have an issue with that sensor.

 

Cool man ill go ahead and do all that I really appreciate for all your help again thanks bro

 

You should really get a scanner hooked up to it now that you've replaced the TPS sensor and have a SES light on. A scanner will also show you the IAC counts and what rpm the computer is seeing. If your IAC counts are 0 and you have an idle speed of 800 that means either you have a vacuum leak or someone turned up the idle stop on the throttle body.

 

the only thing is that the obd port wont connect with the scanner not sure if the there is a fuse for it what do you think any ideas.

 

Yeah check the cigarette lighter fuse.