What causes an engine to stall at idle but run fine over 1000 RPM?

Answer 1

Your throttle body is probably dirty,The throttle body has a hose from the air filter housing attached to it,the throttle body is attached to the intake phlenum.Take the hose off(its rubber with a clamp on it).Do this with a cold engine, NOT RUNNING ! spray some carburetor cleaner inside the venturi and scrub it with a toothbrush,on the side of the throttle body there is a place where a cable goes into,twist the direction of cable to open the throttle plate(inside the throttle body),and continue to clean.Now put it all back together.What happens over a period of time is the Throttle body gets clogged with carbon and cannot breath at idle, the throttle plate when close(at idle)has a very small air gap and cant breath when dirty.If this does not cure your problem,then you will need to consider having your ais motor check.ais= automatic idle speed motor.For this you will have to take the throttle body off to replace it and the screws have been installed with locktight and are tricky to get out. ,I did not know what year or make of car, but its a common problem since the fuel injectors took the place of the carburetors.

• ** Be careful that any cleaners used are for Fuel Injected systems and are O2 sensor safe. Some Carburator Cleaners can damage FI components.**
• Spraying a throttle body spray cleaner, such as one sold by STP, to clean the throttle body, then starting up and revving the engine, may be enough to dislodge the carbon deposits and material blocking the airway. The original poster's solution is the cheap and easy way to handle this problem of low engine RPM causing stalls. Try it first, it is a fast fix, and it worked for me, causing my engine RPM to go up above the stalling level when my car was idling at a stop sign or red light.

I had this problem just two days ago. When the rpm goes below 1000 it stalls; visible black smoke is also observed at the exhaust when it's rev up. Try changing the air filter as this might be clogged up causing an inefficient air/fuel ratio. When there's not enough air going into the system complete combustion is not achieve causing this problem. Good luck. Pls let me know if it solve your problem.

AnswerI had a similar problem. My 97 Jeep Grand Cherokee would run fine whenever I would accelerate, but once I took my foot off the gas, the RPMs would drop to zero and stall. Sometimes it would drop to zero than catch idle out low, but stall again later. I got a $300 tune up that did nothing. The problem turned out to be my IAC motor, or the Idle Air Control Valve which sold for $80 at the dealership ($30 at Autozone). If your car is doing this, replace this part! It would also stall whenever I took a turn slowly or tried to pull into a parking spot. ! Thanks to this forum, I diagnosed this as my problem, and I want to share with everyone else who may be experiencing this frustrating problem.

(addition by LucheLibre) My 87 Jeep Wrangler had the same problem. Did some research and found that older jeeps use very thin idle tubes mounted in the venturi. These can easily become clogged and fuel will back up and come out the main nozzles, causing the Jeep to run too rich and die. The solution is quite simple. Pull the air cleaner housing and choke plate off--remember to keep an eye on how the choke linkages are connected to the carb--unscrew the venturi and pull it out. You can't miss the tubes. Run a long, very thin wire or pin down the tubes and then reinstall everything in the reverse order. Your Jeep will literally be good as new. If the same problem comes up again, then your float bowl is junky and clogging the tubes again. Clean the bowl and change your fuel filter.

AnswerI have a 1996 sunfire 2.2 litre engine that is doing the same thing, i have replaced fuel pump, plugs, wires, fule filter, air filter etc. AnswerThe fuel injectors get dirty and clogged. I add some fuel injector / carburetor cleaner to the gas tank and it usually clears the stalling at idle problem. AnswerI am experiencing the same problem with my 96 eclipse RS. I replaced the air filter- that didnt help, i added fuel cleaner- that did nothing- I have a fule filter but i don't want to waste the money if that's not the problem id rather return it and get my money back! So let me know what works for you guys experiencing the same problem! Thanks a million! AnswerMy 1999 Pontiac Montana would stall intermittently when I would remove my foot from the accelerator and slow down. Dealer replaced the IAC motor and cleaned out the throttle body but the problem persisted. I disconnected the connector to the throttle motor and the air intake dampers and bent the contacts to improve contact mating. Frequency of stalling was greatyly reduced. Next I will clean the contacts to remove oxidation.GM uses cheap tin plated contacts. Answeri had the same problem as the 96 eclipse, but with me 91 Mazda... the main problem was the air hose so we duck taped it up until we buy a replacement. a little bt later the whole engine went bad and the head was warped and had a few cracks. Had that fixed and it ran great, then we started seeing whitish blue smoke from the exhaust... we're going to replace a vacuum modulator and a seal that a friend just added to the car after breaking the new one. We had also replaced several things first and tried the fuel cleaner. Nothing seemed to work or it would run okay for a mile then start up with its bad again. Good luck. AnswerIdle control valve is not working. If it is a fuel injection system, check the fuel pressure controller also as these go hand in hand. AnswerThe "automatic idle speed motor" may also be known as the "Throttle Position Sensor," but it could also be the "Idle Intake Valve." The latter would be the one I would look at, since it's the one that's taking in air while the car is idling, i.e---sitting still with the motor running. If it's clogged, your car will die when it's not requesting power from the engine to accelerate.

Answer:

I've never known an "automatic idle speed motor" to be considered a throttle position sensor. An "idle speed motor" is just another name for an "idle air control valve" or "IAC". I've seen this concern many times. Most of the time it was caused by gunk becoming lodged inside the IAC passage. That's one of the easiest things to inspect at least.

AnswerHave you checked all the corroborator vacuum hoses. That sounds incredibly the same as the problem I experienced with a Honda I owned once, the solution a mechanic showed me was to use a pair of needle nose pliers and slightly clamp on each hose at both ends ( without clamping hard enough to break the hose ) until the engine would idle normally. That said once the problem vacuum hose is located you would merely replace the hose, about a .99$ fix at autozone. Take the hose in with you to compare. Tell them what its for and the specifics to make sure the hose will last.

Another possibility, a stuck open or sticking EGR valve would also cause those symptoms.