Thanks for all the recent help.

When starting cold the rpm's go up above 1200 then fluctuate down once or twice to 600 like it wants to stall then levels out at 1200 while warming up. If I then just touch the gas pedal slightly the rpms drop to 500 for a second then go back up. Once its warmed up its fine. Its getting worse everymorning.
Im just going through checking all the sensor voltages and resistances. So far the Air Intake temperature sensor readings seem fine when cold and after warmed up.


It was running really rough a week ago and I pulled codes related to the eGR and thermactor air system(THE air bypass valve was not getting vacuum).
I recently replaced the EGR valve and had the 2 melted vacuum hoses which i patched and things are now running great. The engine is running fine otherwise.

Any ideas would be welcome.

'90 Bronoco 351 EFI

 

It sounds like it could be the idle air control valve.

 

The good old IAC. That's probably it like the man said. On a cold start my truck idles high for about 30 seconds and then drops down to normal and stays there; also it will drop down and stay if I tap the pedal before it goes down by itself. This is how it is supposed to be. If it fluctuates up and down then there is a problem, probably the IAC. Easy fix.

 

the tps will also do this. i know you said you patched the vacum lines but you probably just need to replace them with vacum hose.

 

ill try the tps first and check the vacuum lines. They are all old and brittle anyway.