Hey everybody I have a 88 gt auto with shift kit it idles rough when u start it up it goes up and down till it shuts down and after you get to driving it will idle at 2000 rpms or alittle more until u shut the car off it has a new iac

 

Check all the vacuum lines for cracks/leaks. Check the Map sensor.Check the gasket for the IAC. MAP sensor bolted to firewall behind engine.

 

Mass air car or speed density? If speed density, any mods? Try checking your tps sensor also

 

Check for vacuum leaks could find any has new iac a new tps and new map sensors and still didn't help

 

Have you checked the voltage on the tps?

 

Yes and that all reads ok

 

Besides the shift kit, are there any mods to the car at all? On a stock 5.0, I would agree it could be vacuum. Make absolutely sure none of those 25+ year old plastic vacuum lines have cracks. Personally, I have replaced at least 3 different lines on my 88.
By the way, when did your GT start showing this behavior? What are your RPM when stopped in gear?

 

Just shift kit flow master cold air intake

 

This.... Discontent the battery and reset the CPU. Do you have and OBI/II reader or know someone that does??

Run Both Key Off/On and Engine Off/On, check the codes... Will save time chasing Fox Idle Issues... I know we have 4 of them..

 

The codes that showed up was a problem with the thermatic air diverter I have never heard of this peice before

 

Check the graphic provided by Td01GT above its on the left hand side.

 

Ok I found it what do it do or control also my altenater is make a noise to that's getting worse could this also cause idle issues

 

The thermactic air diverter is one of the many emission control devices. When I got my '92 mine was bad. I got a new one from latemodelrestorationsupply.com and haven't had a problem since. Be careful, the air diverer solenoid and the air bypass solenoid look almost exactly alike. One is closer to the engine, and one is closer to the fender. Both are about $45. When I replaced mine right after I bought my car (12/26/12) I was surprised how brittle all of the plastic and rubber vacuum fittings and hoses are. I mean FRAGILE. Don't lean on anything that you don't want broken.

 

It would be nice if they had a direct replacement for those plastic vacuum lines.. But I replaced mine with some very nice Fabric lines..

http://www.carpartsshed.com/Catalog/...FTW01331615156

 

Indeed there are no direct replacement vacuum lines. That's why I went through the research and pain of replicating them exactly. I will have them available for sale. Let me know if you want a set. New lines in the correct material, colors and lengths. New connectors. The only part reused is the vacuum connector where the 5 lines meet together.

-Kevin
Bronco_5@hotmail.com

 

Nice! Will contact you!