Stalling and Rough Idle
 

I'm currently trying to bring back to life an abused 99 2.5 5 spd. When I first brought the car home it ran a little rough, a bit of a missfire down below 3500 RPM but it ran well enough to get home. The next morning when I went to fire it up the and the battery was dead. I replaced it later that day and when I started the car it ran incredibly poor. Would not idle, ran very very rough and would stall whenever the RPMs got low requiring constant throttle to keep running.

I just did basic tune up stuff on it now to see if it would fix the problem. New plugs, cleaned the throttle body, idle control valve, and MAF. This made the car run way better. It will idle after start up, but hunt for an RPM. It'll normally run pretty smooth around the high 700 RPM range for a hand full of seconds and then drop down and hunt around 3-500 RPM dipping low enough to dim the dash lights.

Normally the engine can rev up into the RPMs smoothly, occasionally though it will stumble a bit and maybe backfire. The other problem is that it will always stall with no load on after lifting off the throttle. If I catch it and slowly reduce the RPMs it will return to the rough idle. The car doesn't give any codes unless it backfires. When it has done that it threw the codes for backfires on cyl 1, 2, and 3. However that's not every time the car runs. I've checked a bunch of times to make sure I got all the vacuum connections back on and seated properly. I'm not familiar enough with the engine to know what sounds are normal for it but it dose sound like there is a bit of a sucking noise at idle that goes away when you start the step on the throttle.

I'm not sure where to look or what to test next.

To me, ALL of that, sounds like vacuum leak.
Is not uncommon for an older car like this to have brittle and cracked vacuum hoses.

I'd consider doing a smoke test. You can look online and find some pretty good DIY smoke machines.

Good luck! Keep us posted!

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What are the codes for "backfires"? Do you mean "misfire"? A misfire and a backfire can be related but are not necessarily the same.

Please post the exact codes, they can help quite a bit in diagnosis, especially if the problem is isolated to one bank (cyls 1,2,3).

Yeah I'm worried that it's a vacuum leak problem too. I never even thought of making my own smoke machine. I'll look into that.

You're exactly right I mistyped and mean misfire. When I first had the problem it gave me:

P0300 - Misfire damaging to cat. converter and
P0301-P0304

The last time I fired it up it gave me:

P0300 and P0304-P0306

No MAF or O2 sensor codes and sometimes no codes at all.

First, misfires on cyls 1-3 and cyl 4.

Then, misfires on cyls 4-6.

The most common cause of misfires are coil packs, spark plugs, air leaks, MAF, and/or engine sensors.

The hunting idle does suggest an air leak but you said that the car actually backfires which implies a timing issue and that is usually related to an engine sensor problem.

Roger that. I'll keep hunting around. Upon further investigation after work I tried to pop off the oil filter cap and noticed it had no effect in the cars idle, it continued to idle rough. Looking around under the throttle body the flexible filler tube doesn't seem to be leaking but where the hard L shaped tube goes into the crank case is covered in oil and gunk. I ordered that and a new O-ring to swap out. Could that be causing enough of a vacuum leak to cause my problems, or is this just something else that needed to be fixed?

Roger that, I'll keep digging around. Upon further investigation after work I tried popping off the oil filter cap while the car was at idle. It didn't change how the car was running at all, idle continued to hunt and didn't get any worse. I looked harder under the throttle body and found that the hard plastic L shape tube that goes to the crank case was caked in oil and grime at the engine. The middle tube didn't seem to be wet or dripping from anywhere. I ordered a new tube that goes into the engine and a new O-ring to put on. Any ideas if this could be causing the idle and stalling problems I have? Reguardles it needs to be replaced and cleaned up, I'm just hoping this will fix the problem.