2.9 Rough Idle/Stall During Warm-Up

Hi...just joined. My ride is a low mileage 87 Ranger 2.9 with the A4LD trans. If I just start and drive without slowing down to an idle until it warms up fully, there is no problem. However if I'm doing stop and go and it's only partially warmed up, it will go suddenly into a rough idle condition and sometimes stall. I've noticed black smoke out the exhaust when it does this, not always but occasionally.
I don't have a code reader and was hoping I could avoid the shop cost of having the codes read, by finding someone on this forum that could give me some things to try without spending a bundle. I got some wrecker components and tried them with no improvement. These include the TPS, IAC, MAP and a weird vacuum device on the passenger side fender near the starter solenoid. I have no guarantee that any of these components were good so I'm prepared to start over if someone has some suggestions from similar experience.

Just thought I'd re-post this problem so it gets back on the front page...hope I'm not breaking any forum rules here.
Quite a number of views but no replies yet. Maybe I've got one of those complex problems that nobody can help with. I appreciate that intermittant engine problems are sometimes next to impossible to diagnose. I did manage to pull some codes and got an EGR fault. I actually removed the EGR and plugged all the lines, hoses and port but there was no change to my 1/2 warm rough idle.

It sound like you're knowegable and on the right track, just one of those harder-to-find problems. A couple of things to note would be that you mentioned that you get a puff of black smoke. That indicates too much fuel rather then lean, or oil (which would be more blue but hard to tell sometimes) which can come from a couple of places. Check your PVC valve carefully as that can also give you a vacuum leak and cause the poor running condition. Since you have the autotrans there is a small possibility you could have a leak from the vacuum diaphram. Other things to check would be the O2 sensor, and an ignition problem could certainly do this..

If your vacuum lines check out (your other post) then there are other 'hard' problems that might be happening, (assuming the engine is fine internally). The intake manifold gaskets do have a historic problem of leakage and many times can be fixed by just re-torquing.

I know, I didn't give you the majic bullet, but hopefully you have a few more places to check...........

Good tips, much appreciated whisperer. The PCV rattles when shaken and is not fouled, just varnished. If I plug the end of the PCV with my thumb with the engine running, the engine stumbles. So I think the PCV is OK.

There is a black plastic breather on the drivers side valve cover that is hosed to the TB. The protruding tip of this breather (about 3/4' dia.) is partially broken off. I'm wondering if there was a check valve in there and now it's missing. Are you familiar with this breather ? I think it works with the PCV to let fresh air into the crankcase so that the PCV can pull blow-by out of the crankcase and into the intake. Kind of a closed loop recirc. system maybe ?

The modulator valve is new so I don't think there is a leak at the diaphragm.

I actually have the O2 sensor unplugged at the moment because one of the 3 wires was boken off anyways. I was hoping that it wouldn't make it run much different because the other sensors take over in open loop anyways, until the O2 sensor heats up and goes into closed loop. Am I wrong in assuming that the O2 sensor really doesn't affect significantly the way the engine runs, but really only fine tunes the injected fuel volume for optimum emissions ?

Hope I'm not wearing you out, but what kind of ignition problem would you think suspect ?

Never thought of intake bolts being lose. Will tighten those as a next step.

Thanks again for the tips and your time.

Yes, definately get the O2 sensor hooked back up correctly. That is the final input that the computer sees and adjusts all the parameters accordingly.

The vent fitting on the left (drivers side) valve cover is exactly as you said. That line terminates directly in front of the blade on the TB. Even though it is before, it is like 1/4" before so it is possible it could make a difference, but not highly likely.

Ignition related could be anything. I'd first suspect spark plugs and cap/rotor, then wires. Somehow, (OK, I'm generalising now) people seem to think that "gee whiz, I have electronic ignition and platinum plugs so it's fine forever". Not so, distributor caps wear out quicker then they used to with the high energy systems. Wires actually go bad before they fall apart instead of visa-versa like they used to. Coils burn up the towers regularly (where the coil wire goes). High energy ignitions just eat themselves up, and THEN they save themselves by being able to fire across that missing electrode, bad wire etc........

OK, I guess I'll fork out for an O2 sensor (thought I could maybe avoid that since the truck is now past legal emissions requirements age here in Ontario). Thanks for educating me on the O2 sensor's actual function for the computer. I got that "runs OK on open loop" theory from another forum.

I'll get a new vent breather just in case. They are only $10.

I was hesitating on looking at the distributor, partly because I didn't think I had an ignition problem (the problem occurring at a certain time part way thru warm up, ie. intermittant), and also because the distributor looks so awkward to work on being located so close to the firewall and tucked under the upper plenum.

I pulled the plugs last night and found the electrodes and insulators to be clean but very white in colour. Haynes says they are running too hot. They suggest possible incorrect plug heat range, over-advanced timing, lean fuel mixture, intake manifold vac. leaks (I'm starting to see a picture now), sticking valves or insufficient engine cooling.

I'll tighten the intake bolts, install a new O2 sensor and vent breather and see what happens. I'll do one thing at a time so if any one item is successful we'll know. I'll keep you posted. Thanks so much for the continued interest and support.

Sorry I can't help with your problem, but if your throwing a check engine code most autoparts stores will read it for free, no point in paying a mechanic. Or you could just buy one they aren't that expensive usually around $40

Actually I can read codes. There's a nifty way to do it with a paper clip and a test light where you jump a single trigger connector with the paper clip, and connect the test light to the battery pos. and then to the main test connector. The connectors are under the hood near the starter solenoid. You just count the test light flashes and it gives you the 2-digit codes that you can look up. ie. 3 flashes, pause, 2 flashes is code 32. Can direct you to a site that has exact procedure and a diagram if you want.

Quick update: Tightened the 12 intake manifold bolts. Got 1/4 turn out of about 6, 1/2 turn out of about 5, and 3/4 turn out of the lower intake bolt near the fuel press. regulator. They are quite easy to get at.

This did improve the engine's smoothness and the 1/2 warm rough idle is less pronounced and actually tolerable. I must have had a vacuum leak, probably the lower manifold at the FPR. Think I'll just run that way for a while.

Thanks for everyones' help, especially whisperer.

Had an '86 STX that developed the same problem. After about a week of searching I found one of the wires for the O2 sensor shorted out on an aftermarket exhaust clamp. A little black tape and a zip tie... problem gone.

chbtech said:

Actually I can read codes. There's a nifty way to do it with a paper clip and a test light where you jump a single trigger connector with the paper clip, and connect the test light to the battery pos. and then to the main test connector. The connectors are under the hood near the starter solenoid. You just count the test light flashes and it gives you the 2-digit codes that you can look up. ie. 3 flashes, pause, 2 flashes is code 32. Can direct you to a site that has exact procedure and a diagram if you want.

Click to expand...

Could you post that? I do not need it at the moment but I know I will eventually!

Go to The Ranger Station site, Tech Library, Computer, EEC-IV Diagnostics. Read the Analog Voltmeter Method (I use a test light instead of a voltmeter). Click on Test Hook-ups.