89 F150 stalls at idle / low RPM's

If you have not already done it, you may help it by cleaning the throttle body and the IAC since you mention oil in the intake. (This may be a sign of excessive blowby or crankcase pressure. I believe that engine may have a filter in the block under the PCV that may be plugged - not sure.) You will need a can of throttle body cleaner and an old tooth brush to clean the throttle body. You will need to remove it from the intake to do a decent job of it but, you may get some help by having someone hold the throttle open for you while you do the dental work.

The IAC is attached to the left side of the throttle body. It will also need to be removed to properly clean. It may require soaking the valve end - not the motor end - overnite in the solvent to clean it. Check it electrically to be sure it has about 9-11 ohms impedance. That doesn't mean it will work - just means it ain't open or shorted.

After you do this, disconnect the battery for 10 minutes and go have a cold one. Reconnect the battery and start it w/o touching anything. Allow it to warm at idle and then move the trans selector amoungst all the trans positions several time for several seconds each to allow it to relearn it's odle paramaters. Drive it around town a few miles and see if all is well. If not, there are some other things that may need attention.

The whirring noise you hear may be the a/c system equalizing if it has been running.

Good luck Lugnut

Thanks! IAC it was. It puurrrrrrs at idle now!!!

Well, it appears that the multiple symptoms that I described were caused by multiple problems. After driving around for a while, the truck started to stall again at freeway speeds and even died at a stoplight. The idle was still solid, but it was running rich and cutting out.

I bought a computer code reader ($35 at Walmart) and a code 33 (EGR Valve not closing properly) popped up during the KOER test. I replaced the EGR Valve and it seems to be running much smoother. But, I haven't had the opportunity to get it over 45 yet. One good thing is that the new EGR Valve has quieted an engine knocking that was happening durring acceleration. It's not gone, but it is MUCH better.

Thanks again for your help. I'm not even close to being a car guy... this forum is very helpful. I'll continue to post updates/questions if anything more happens.

More often than not, the EVP sensor on top of the EGR is bad instead of the valve itself. It tells the ECM exactly how far open the EGR valve is at any given moment. The EVP sensor rarely results in a fault code as it is just barely in the adaptive range of the ECM but, far enough out that the function of the EGR system is inadequate. This makes the position of the EGR near the edge of acceptability. The EGR valve was probably OK if you could disconnect the vacuum line w/o noting a change in idle quality. If you have a source of vacuum, you can apply vacuum manually to the valve. If it then stalls the engine, it is probably OK. An EGR valve that is not opening far enough can cause both a limited rich condition and "pinging".

Your rich condition may be caused by a bad fuel pressure regulator as they had a fairly high failure rate in that vintage. If you pull the vacuum line and find fuel, it is definitely bad. A fuel pressure check should show about 35 psi idling. When you open the throttle, the loss in manifold vacuum should result in an increase in fuel pressure to 40-45psi. I've seen a completely failed regulator result in fuel pressure over 90psi which will quickly result in a failed fuel pump or other problems. If you rev the engine and suddenly close the throttle to create high manifold vacuum, you should see the fuel pressure drop to 15-20psi. You can, of course check this with a vacuum pump and guage along with a fuel pressure test guage. Normally, if the regulator fails, the fuel pressure will go high and not drop when vacuum is applied. In my own f150 w/5.0L, I saw fuel mileage drop to less than 9mpg when the fuel pressure regulator failed on a trip - it was typically in the 17-19mpg range on the same trip.

Another common item that can cause a rich condition is the ECT sensor (engine coolant temperature). It tells the ECM the engine temperature. A sensor with an incorrect value can tell the ECM that the engine is warmer or cooler that it actually is. This will result in a rich or lean condition depending on which way it is out of spec.

Another place to look for a bad or erratic idle on those is a vacuum leak between the upper and lower intake manifold. They were known to occasionally suck a gasket especially where someone did not properly torque the upper plenum. You can usually find this by spraying something like WD40 or carburetor cleaner along the joint with the engine idling and listening for a change. Some folks like starting fluid (ether) but, you can also damage the engine if you get a big slug of ether into the engine thru a leak. You can also get yourself blown up if Murphy is upset with you on that day.

If the upper intake has ever been off, check the small plastic vacuum lines behind the manifold. They are super easy to get pinched and broken when tightening the upper intake. This can also warp the casting a bit. Since those lines are for the EGR, the may play havoc with that system as well as causing a vacuum leak that affect engine operation.

Good luck Lugnut