5.0 Nearly stalling...

[ZackN920]

Trying to figure out why it does this...

Today, backing the car back into the garage/pole building I legitimately thought it stalled on me... Then it came back to life There is a little ridge at the bay doors, if I'm going in slowly it stops the vehicles in it's track's, and then I lightly blip the throttle to get the vehicle over it. When I let off the gas, the car really dipped in the rpm's. This has been an on going problem for the car while I have owned it. It doesn't seem to matter if it is cold or warm, when ever the throttle is blipped lightly while in gear, the engine will almost stall and then catch itself before it actually does. Why does it do this when it runs great in every other way? Gets good mpg's too.

It will also occasionally do this when shifting into a gear. No throttle applied, just shift it and the rpm's drop for a sec to the point that it sounds like its going to stall, but then catches itself. Mostly when cold, but has done it a few times at operating temp.

Normally, with my carb'ed vehicles it's a mixture problem. Most times, too lean of a mixture. Is that usually the same deal with the fuel injected engine in this situation? Do I most likely have a vacuum leak? Or is there a sensor that could be failing? What do you all think? I haven't really dealt with this before on fuel injected vehicle.

[Kodachrome Wolf]

Might be worth cleaning the IAC and seeing if the condition improves.

[87GrandMarq]

I second the iac. Do you know if the throttle stop screw has been messed with at all?


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[bgreywolf]

I third the IAC/throttle cleaner spray (don't scrub the throttle bore, just rinse with a bottle of injector cleaner). Also check the base idle timing and speed (engine warm, steady idle, SPOUT plug removed, as described in the base idle setting procedure).

[gadget73]

What they said. If the idle controller is stuck it won't compensate for changes in load.

[ZackN920]

Thanks guy's for the IAC tip. Totally forgot about that... And to think, I had to replace one in the Cherokee because it went bad. It would stall when I came to a stop, unless I held the gas, and idled like shit when in P or N. Tried cleaning that one, it didn't take. Actually made it worse...


Well, I took the IAC off and found that it really wasn't bad. Everything still moved around good, and wasn't too sooty inside. I took the solenoid off and cleaned the pintle assembly out with throttle body spray I still had laying around. Put a new gasket on and put it back on the throttle body. Still isn't perfect, but the engine acts better than before. No more "nearly stalling" if I blip the throttle a bit. After I did that I drove it into my shop and put it up on ramps. Gave it an oil change for the upcoming season. Engine must be a bit dirty inside, oil was only about 8 months old, only about 2.5K miles on it and it was as black as could be... If I get to resealing the intake manifold this summer (and hopefully add an HO upper) I'll probably change it and the filter again and see how it looks.

Do you know if the throttle stop screw has been messed with at all?

I really don't know. PO was an old guy that I'm sure didn't do work himself on it.

I third the IAC/throttle cleaner spray (don't scrub the throttle bore, just rinse with a bottle of injector cleaner). Also check the base idle timing and speed (engine warm, steady idle, SPOUT plug removed, as described in the base idle setting procedure).

This will be on my to-do list for tomorrow. All Ive done so far was take off the IAC.

What they said. If the idle controller is stuck it won't compensate for changes in load.

Ok. That makes sense.




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Just an observation. When googling around some about the subject, I came across a post here with someone saying that the engine should still run if the IAC is unplugged. Just that it would drop to 500rpm or so and nearly stall/ run rough in gear. So, for shits and giggles I tried that before I took the IAC off. Now, in my situation I don't know if it matters but with the IAC unplugged, my car would not start. If I tried to start it like a carbed car (with throttle held lightly open) it would start. It would stay running just fine too, as long as I had my foot on the throttle. But, the second I let off it would immediately stall. I should also point out that the car was cold, so I don't know if that would matter that it was running in open loop or not.

[Tiggie]

Turn up the idle/throttle stop screw until it will just barely idle without the IAC plugged in.

[Kodachrome Wolf]

Just a side note, if you do have to adjust the throttle stop, you may need to also make an adjustment to the TPS since you may take it out of range. IIRC, the acceptable range for closed throttle is anywhere between .5-1.25v, but most folks set it in the .8-.99v range.

[gadget73]

Definitely change the oil if you remove the lower intake. I blew up an engine doing that once. It will dump a bit of water down the galley, and it was enough to wipe out what was left of the original bearings on my Towncar's original engine. I'm sure they were just about hanging in there anyway but within 20 miles of that lower intake job I had no oil pressure when hot.

[ZackN920]

Turn up the idle/throttle stop screw until it will just barely idle without the IAC plugged in.

So, I take it the engine is not supposed to rely on the IAC to idle/run. I wonder how it could've gotten "off" like that? Should I just go ahead and adjust it, or should I maybe disconnect the battery for a bit, then reconnect and start the car and let run for 10 minutes? Then see if the computer "re-adjusted" to run properly as is?...

Just a side note, if you do have to adjust the throttle stop, you may need to also make an adjustment to the TPS since you may take it out of range. IIRC, the acceptable range for closed throttle is anywhere between .5-1.25v, but most folks set it in the .8-.99v range.

Really? The TPS is adjustable on these? huh. I'll have to see how to measure that voltage first to see where im starting out at and what I end up with if I do adjust it.

Definitely change the oil if you remove the lower intake. I blew up an engine doing that once. It will dump a bit of water down the galley, and it was enough to wipe out what was left of the original bearings on my Towncar's original engine. I'm sure they were just about hanging in there anyway but within 20 miles of that lower intake job I had no oil pressure when hot.

DAMN, that sucks! If that's the case ill probably flush the engine out with cheap oil right after and then change it again just to make sure its all cleared out.

[sly]

Idle set procedure for the 5.0L SEFI is the same as the trucks, but no feeler gauge needed (skip step 1) and set base timing between 10 and 14 degrees for most vehicles. If yours pings afterwards, reduce base timing (factory is 10 - the 88 MGM I used to have liked 14-15 degrees a LOT better than 10 and wouldn't ping until about 17-18 based on the balancer on it It could have spun a little - never checked).

[gadget73]

Good, I didn't have to scan that out of my manual that says all the same stuff.

yeah, base idle reset process. Whee. Usually the only reason that has to be touched is if someone touched it in the past. Usually. Also make sure the base ignition timing is correct before doing this or it won't work correctly.

[ZackN920]

Hey all, been awhile. I got access to the internet again so I can reply. Thanks for the above info. I read it while visiting someone back when you guys posted it.

Anyways, I adjusted idle speed and the tps sensor right after I made my last post. For the most part, my problem with the idle dipping down when changing gears has been solved. I never did check the voltage of the tps, I just adjusted it by ear/tachomter that I connected. To be honest I still haven't checked the timing yet either. It just runs so good that I haven't wanted to really bother until necessary . So, for the last 2 weeks now I've been daily driving it when I haven't needed the pickup truck. Its running good and seems to be getting pretty good in town mpg's. Good power and response(little better now after adjusting the tv cable a bit tighter).

One problem has popped back up though... Just like when I first got the car, it is having a long cranking problem, but only when warm. When cold it starts fine, but after it has ran and been off for awhile, if I go to restart it without cycling the key a few times it will crank a good 5-10 seconds before it will fire up. Lately I have just gotten in the habit of cycling the key 2 or 3 times before I try starting. It fires up immediately after doing that. Would this issue be at all related to the original problem that this thread is about? Or my fix for the problem? Or is this completely unrelated?

[gadget73]

sounds like the check valve in the fuel pump might be ailing and causing the fuel pressure to drop off too quick after shutting down. Might be worth doing a fuel pressure test just to see what it does.

[DerekTheGreat]

Fuel pressure regulator too, check that. Ashley's was bad and sometimes she'd have to crank for a while too. Guy we sold it to replaced it and said it started it just fine after that. My '88 started instantly this morning, I wonder why they do that sometimes. Smooth riding old thing, how can I sell it?