What could cause a car to stumble and die at idle?

I know, I know, over the phone diagnosis and all.

I have a friend with a 1997 Jeep that dies while sitting at a red light. She knows where the gas goes in and how to open the hood, but that's about it. I think I may end up spending time with it next week. What do I look for?

It stumbles, idles slower and slower, then croaks. Gas, air, spark, I'm guessing fuel delivery. I asked if it was carbed or fuel injected, she has no idea.

Check list:

Fuel filter.

Air filter, clean airway.

Carb cleaner or injector save-the-baby.

Timing?

Anything else?

Thanks, Dan

if it restarts and accelerates okay I would not think fuel. I would think air.

vacuum leaks. (if it is automatic then she is sitting on the vacuum-assisted power brake pedal at stoplights... hint hint)

On my 89 jeep (4.0) I broke a tiny plastic vacuum line while changing the fuel injectors. It ran like absolute dogpoo until I used a small piece of vacuum line to connect it back up. Must've been a line to a manifold pressure sensor or something.

My point is that even tiny vacuum leaks in the wrong places can wreak havoc.

If it's fuel injected, vacuum leak or bad MAP sensor. Does that jeep have the 2.5 or the 4.0?

Vacuum leak, MAP sensor, or O2 sensor. When my '95 Neons did that, it was O2 sensor time.

Wrangler/Cherokee/Grand Cherokee? 97 jeep means nothing without the model. you could have the 2.5, 4.0, or the 5.2. all efi and all obd2. it should be throwing a code of some sort if it is just dying.

Idle speed motor, throttle position sensor, egr valve, dirty throttle body, etc. Does it actually die as she is sitting, as she is slowing to a stop, or when she steps on the gas top accelerate away?

My Mazda3 did this. In my case, I had to clean out the throttle body as others have suggested. Mazda issued a TSB on this as it is fairly common.

Like many above said, I would first check for vacuum leaks. I had this issue not too long ago. My F-150 would run fine when I was on the throttle but whenever I came to a stoplight it would have a terribly rough idle and many times would die. I ended up finding a small PCV elbow behind the throttle body was cracked.

I would next clean the throttle body.

Everyone above has said valid things that could have gone wrong. If it's none of those, the last thing I would check is the crankshaft position sensor.

06HHR wrote: Does that jeep have the 2.5 or the 4.0?

It's blue.

IAC !

Tell her to push the clutch pedal in when she comes to a stop.

Lack of ambition?

HAHAHAHAHA @ Wally and TJ

Take a can of throttle body cleaner, remove the intake hose from the TB, locate the IAC bypass port, start the engine, with one hand on the can and the other on the throttle(to keep it running) spray the cleaner through the IAC passage. Clean the TB while you're at it if its filthy.

I will definitely say IAC is the first thing I would check. Its two torx screws on the TB, and my guess is its all gunked up. Use a wire wheel on your grinder and polish off all the crap and re install. Can't hurt to pull off the TB and clean out the seat in there and generally get gunk out.

Next place I would look (if its the 4.0L) is the crank position sensor. The wires develop cracks and intermittent shorts (and they're known to just fail internally too). That usually shows up as long cranking before starting on the other models, but can confuse the ECM particularly on the 4.0L.

Third place I would check is pull the vacuum line off the fuel pressure regulator and start it up. It may not run, but it will be a long enough time with fuel pressure to see if its bad. When they fail, they often push fuel out of the vacuum port on the regulator. On the highway, it doesn't make much difference, but a little bit of liquid fuel getting sucked in the intake will cause it to stall.

Wait... I lied... the first thing I would check is its resale value, then I would check out the black friday sales at dealerships.

(not a fan of early OBD2 jeeps/mopars)

Kenny beat me to it. Especially if it's the 5.2. I used to keep a can of toluene and a clean rag in my Dakota for that reason.