Stalls when warming up

[Slartibartfast]

I've looked around a bit, and didn't find much. If this has been asked before, and you must therefore kill me, please make it quick.

 

We've had a few cold days, but not much below freezing. I did add gas to it recently, where I usually get gas with no problem. Prior to this, it was running just fine, save a little exhaust leak and a whirring bearing somewhere. No overheats, rad cap looks okay, no stalling, and the only recent engine work we'd done was tightening a fuel line. I had the battery disconnected a few times the other day when I relayed the lights. Yesterday I left my lights on at school and drained the battery so bad the stereo forgot its presets, but not enough to kill the dash clock. Obviously it didn't start (I did try, it didn't even click), so I got a jump, let it idle a few minutes, and drove it home (a few miles, mostly highway).

 

It died when I slowed down to turn off the highway, then died again when I restarted it. By keeping my foot on the gas, I managed to get it out of the road, back to my house, and into its spot. At my dad's suggestion, I let it idle a while, hoping that would charge the battery back up. It struggled to maintain idle, so I sat in it with my foot on the gas for maybe twenty minutes off and on. When it could idle without help, we thought it was fixed, and shut it off.

 

I took it out again today. It worked fine while cold, but when it got a little warm it couldn't keep the engine going if my foot wasn't on the gas. I drove it a block or two to school with two feet. It stalled at stop signs, it stalled when I tried to pull out into traffic, and when I parked it, the idle was falling, struggling, and surging again. It's like it's not realizing that it's dying until it hits 200 rpm.

 

It seems to run fine when it's cold, but when it's partly warmed up, it can't keep its idle up. It stalls at stop signs, on sharp turns, whenever my foot's not on the gas. Parked, it idles at 8-900 (normal), then drops way down, struggles (the dash lights flicker when it's struggling), then revs back up to 1k, then falls again. But if I keep pushing it, it reaches operating temp, and it's fine.

 

It runs great cold, it runs great hot, but it won't idle when it's in between. The thermostat was probably replaced a few years ago with the timing belt. We've ruled out the battery. My dad says he thinks it's got a little vacuum leak somewhere, and suspects this is a choke issue or wet gas. He also said it didn't feel like it was running right until it's hot, which I didn't notice, possibly because I was freaking out a bit. The only time it stalled before this was when it was really, really cold. I've tried unhooking the negative cable to reset the ECU, thinking maybe the brownout or me turning the key when the battery was flat had confused it, but this didn't help. The CEL's not lit. It's not warm out, but it's not appreciably colder than it was before I killed the battery.

 

I know it idles higher when it's cold, and is more efficient when it's warm, so either it's not choking right, or it can't choke enough to compensate for not running right. Vacuum seems probable, but doesn't explain the sudden onset. But how'd I do this by killing my battery? And, more to the point, how do I fix it?

Edited November 11, 2011 by Slartibartfast

[trogdor]

That does sound like a vacuum leak and those happen pretty fast some times. not sure on the 95 pathfinder vacuum systems but i would retrace your steps from when you had the battery unplugged and the fuel lines done pathfinders have obscure vacuum lines and maybe some where you have a wire that is shorting out...

[adamzan]

In the FSM there is a complete vacuum line diagram in the EC section I believe.

 

A few other things to try:

 

unplug the o2 sensor and see if its better

check the voltage or w/e the fsm tells you to do to the coolant temp sensor.

wiggle the maf wire when its running bad.

[Trogdor636]

Mine is doing something similar every now and then, and I believe my problem is my TPS. I've actually wiggled the wires, and tapped on it with a screwdriver and then it runs fine for a while. Then again, with the few cracked vacuum lines I've seen, I think its time to replace all those too.

[Slartibartfast]

Thanks guys, I'll check my TPS, then see if the hoses are okay. I doubt it's the 02, as it wasn't even connected until I realized a wire was broken, and performance didn't seem to change afterwards. I'll tear into it Sunday night or Monday and let you know what I come up with.

[1994SEV6]

Yeah, this definitely seems like an oxygen issue. Vacuum lines will make your engine do the craziest things if they are faulty. It's so weird how those work.

Pretty much as the people above said, it's going to be vacuum lines, the MAF sensor or possibly the O2 sensor.

There is a post on here about cleaning the MAF sensor. You should go ahead and do that, even if you weren't having this problem. After that, just check hoses

[Slartibartfast]

Got back into town last night, drove it to school and back today, and it didn't give me any trouble. My dad took it out before I did and didn't have trouble either. He suspects he jostled the TPS when he tried to check the air filter, which makes sense with Trogdor hitting his with a screwdriver. I unplugged the TPS and MAF, made sure the pins were clean (they were) and put some dielectric grease in there just to be safe. It started and idled fine afterwards, and though I didn't examine all of them, the vacuum hoses I did see looked good (no cracks).

 

So, it was probably the connector getting loose with age. I had the same thing with a headlight when I did the relay mod, one was really dim until I bent the pins a little so they'd make a better connection.

 

Thanks for the ideas guys, hopefully this is the end of it.

[Trogdor636]

Got back into town last night, drove it to school and back today, and it didn't give me any trouble. My dad took it out before I did and didn't have trouble either. He suspects he jostled the TPS when he tried to check the air filter, which makes sense with Trogdor hitting his with a screwdriver. I unplugged the TPS and MAF, made sure the pins were clean (they were) and put some dielectric grease in there just to be safe. It started and idled fine afterwards, and though I didn't examine all of them, the vacuum hoses I did see looked good (no cracks).

 

So, it was probably the connector getting loose with age. I had the same thing with a headlight when I did the relay mod, one was really dim until I bent the pins a little so they'd make a better connection.

 

Thanks for the ideas guys, hopefully this is the end of it.

If he was checking the air filter, he could of just as easily been the MAF. In fact, from what everyone on here has issues with, it was most likely the MAF. Mine just happend to be the TPS.