Hi gang. My '89 recently (2 weeks ago) started running like crap when I first start it up. Normally I start the truck and it idles smoothly at 600-700rpm. Now it starts and stumbles down to 400 or lower, cycles back up to 600, back down to 400ish and then smooths out. That process takes about 10 seconds to complete, after that it runs great as usual.

You can expedite this process by giving it some gas either before or after you turn the key. Then it will go to about 1,000rpm (just depending on where you hold the throttle). If you do that for about 5 seconds it will smooth out from there.

It sounds like it's cammed up like crazy while it's doing this and with either method it smells like gas, like unburnt gas.

It throws these fits almost every time I start it and once it does it in a day it will do it every time, if I let it sit for 5 minutes of 5 hours it's going to do it again.

A couple of hints;
The exhaust manifolds are warped and leak, they tick and let in fresh air. As you know, this throws off the oxy sensor and i'm sure at 24yrs old and about 160k miles has all but clogged the cat up.

I had a problem with the truck dying randomly a couple of months ago. The shop said something was broken inside the dizzy and I had magnetism where I shouldn't. They put a used dizzy off the shop owner's old truck and a new (but not Motorcraft) ignition module on it and it ran fine. Ever since then it will try and stumble a little bit 2-3 times on a cold morning but not right away, most often it starts after I leave my cul de sac but ends before I hit the main road 1/2 mile away.

Once the fit is over she runs great, no other problems with power, hesitation etc.

Any ideas?

-Joe-

 

Bump, anyone?

 

I would look at the Fuel Pressure Regulator first. Pull the vacuum line off the nipple on top and turn on the key with a cold engine and see if any fuel comes out of the nipple.
If any fuel comes out it is bad.
The other possibility is a bad fuel injector.

 

I will check that out for sure.

A local mechanic told me he thought it might be the Idle Air Controller, what do you think about that?

Thanks!

 

You could try taking the IAC off and cleaning the crap out of it with carb cleaner. I did that and it idles great now, It had the same problem as yours

 

pull the codes....


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