'90 5.0 low idle, engine light problem

[Cucamongan]

I have a '90 FSB with a 5.0 that I recently had the heads rebuilt ( I stupidly bought it not running and later learned it had a burnt valve) after about 200 miles of the completion of the rebuild, it has developed an idling problem.

What happens is that it starts within the first or 2nd crank and revs higher (about 2000 RPM, on cold circuit) and, (now this is where it acts abnormally), then drops down to about 450-500 RPM instead of the normal 800 RPM. The Check Engine comes on and stays on until I rev it, any amount. Since it idles so low, it sometimes dies (probably becase its idling so low, low power). It drives fine and acts like it has all its power.

Before I before going and replacing tons of parts, the burnt valve did blow oil around the intake manifold (dumb Smog Crap). BUT my real question was what component needs to be cleaned/replaced and what does it look like? (So I dont clean/remove the wrong part... speaking from experience)

Is it my MAP sensor? Idle Air Control? Throttle Position Sensor?

(I have spent an hour and half reading others postings, but never found one exactly like my problem.)

Also, I have a cheap code reader, and I put it on, but it didn't pull and codes. I suspect its me, but then again the check engine light goes off as soon as I touch the throttle.

Thanks for you help and input!

- Cucamongan &lt

 

[Swat]

Probably your TPS but could also be the IAC. The TPS is easily adjusted and it is a good idea to clean the IAC and throttlebody. This is an excellant site to get codes and tech. http://www.fordfuleinjection.com Look under sensors, TPS, IAC..........etc etc. Goodluck!

 

[fragmouth]

Sounds a lot like the same prob I'm having now, only I've waited until the prob is extremely bad - to the point I have to continuously keep one foot on the gas or the engines dies. Lots of dark smoke with a very rich exhaust smell. Turns out the catalytic was clogged completely. I spent today "cleaning" the cat and reinstalling - temp fix for a few weeks until I can scrape up the cash for a proper replacement, lol.

 

The way I found out is I hit the bottom of the cat, with a rubber mallet a few times, and then started my truck. The engine idled correctly for about 15-20 secs then went back to choking-out. Mine is an '89.

 

Hope this helps.......

 

[firelt90bronco]

My 90 has avery low idle too, sometimes you can hear it rev to stay running