My father in-law has a 1998 Lincoln Navigator with 160k miles. He brought it to my house so I could change his P/S pump which was making noise at low RPMs when turning the wheel. No biggie, right? So, all I do is move intake plastic out of the way, take off the fan/shroud, remove belt, pull off P/S pulley, disconnect P/S pressure hose, remove P/S pump, install new pump and new pressure hose, install pulley, put on new belt, put on fan/shroud, replace intake system, start truck. Here's the problem.

The truck starts for a split second like normal and then just dies. If I give it gas, it will run at whatever RPM I give it, so it is getting gas and has good ignition. When I let off the gas, it drops to around 100-200 RPM and will sometimes jump up to 1000-2000 RPM for a second like a surge and then back down to the 100-200 RPM range and then just die. No CEL when its running, either. So, now the truck is immobile at my house and I look like a crappy son-in-law know-it-all shadretree mechanic!

I searched the internet and found a few fixes for this description, so this is what I tried:

I disconnected the battery and reconnected to try and reset the idle trim, no luck.

I removed the IAC valve and cleaned it and moved the mechanism back and forth, no luck.

I removed the PCV hose system that goes from the passenger valve cover then Y's to the either side of the throttle body and inspected for leaks, none found. The PITA one on the back of the intake where it goes from skinny to wide hose is OK too, and mine doesn't make an elbow, it just reduces straight.

I wiggled and disconnected and reconnected my crank position sensor, no luck.

I cleaned my MAF with MAF cleaner, no luck.

Now, without a CEL, I am kind of at a loss here. Any suggestions?

I've posted this in the 5.4L forum as well...

 

Replace the IAC valve.

 

I assume it was running fine before you pulled it apart? If so, I'd say you have an air leak in the air intake ducting after the MAF sensor, or your connection to the MAF has been lost.

 

Yeah it was running fine. Drove about 45 mins to get to my house. He had it in park and moved the wheels back and forth so I could hear the P/S pump make its god-awful sound, and then we pulled it into the garage so I could work. I didn't touch anything besides what I described, which is why I am so pissed about this. Wouldn't a faulty MAF connection throw a code and CEL though? I couldn't get the MAF sensor to disconnect under the air filter, so I just kind of laid it there out of the way. Think I may have loosened a wire in the MAF sensor connector inside the plastic tubular housing??

 

Try unplugging the MAF connector and plugging it back in again.

 

Now I've heard of people unplugging the MAF and turning on the truck to see if it runs better. If when plugged in it runs bad, you know its faulty. Should I do that? Or should I just unplug and replug and then start?

 

First try the unplug/replug/start method first.

 

Guess I have my marching orders!! Thanks guys, and I will report back tonight after I try this. I really wish it would've thrown a code to tell me this though.

 

A bad MAF or MAF connection will set the check engine light.

 

sounds dumb, but are you sure the "new" ps pump isn't bad? If it's dragging it could be putting enough strain on the engine that it won't idle, but you can overcome it by giving it gas. I'd try taking off the serpentine belt and firing it up for a little bit (not more than a minute or so) and see if it'll idle then. Is it possible that you hooked the P/S hoses up backwards? I doubt that because they should be different fittings, but just a thought.

Anyway, try taking off the serpentine belt to eliminate the P/S system causing problems.

 

well I thought the new belt was too tight so I put the old stretched out belt back on with no change. The new pump turned fairly easily by hand so I doubt its that. I will certainly try your idea if I can't get the MAF ideas to work...

 

bad MAF connection! I wiggled the wires that are going into the plug that connects onto the MAF, and the truck started, although it kept surging. So I tried and move the wires enough to allow a steady idle, and it did. Now I just need to make it stay without me touching it. That plug isn't the easiest to work with. Can that whole connection line be purchased?

 

You might try a junk yard.

 

Maybe the contacts are just dirty. Get a can of electrical cleaner (auto parts store) and spray the connections real good. Then put the connector on and take it off a few times and you might be good to go.

 

OK I will try that too. I fiddled with it some more last night and I couldn't get it to idle correctly, so I tried running the truck with the MAF unplugged and it made almost no difference! When I start the truck it seems to fluctuate from around 500-1500 rpms in about a 1 second surge pulse. I left it running for awhile and the pulsing never quit. I didn't dare try backing out of the garage or anything yet.