Engine Surge at Idle


Asked by dtl504 Sep 01, 2009 at 08:37 AM about the 2002 Mitsubishi Galant ES

Question type: Maintenance & Repair

Car runs fine once she is going but at idle the engine seems to surge/buck forward when idling at a stop sign or red light.

6 Answers

Rishi Patel

It could be a few things... the first thing you should do is change your spark plugs, if that isn't it it could be a dirty mas air flow sensor which you can clean or a bad air filter... if its not any of those it might be your idle air control or a few other things. Try the first three and see how it goes.

4 out of 4 people think this is helpful.
Matt Rodriguez

Might even be your Throttle Position Sensor, but just go down the line with the least expensive fixes first like Rishi recommended and troubleshoot those one at a time until all is well again.

2 out of 2 people think this is helpful.

I had this same annoying problem over several years, high revs in idle and surging. Took it to all the experts and auto electricians charged me but never fixed it. So after removing the throttle body from the aluminium air manifold on top of the motor made up a new gasket from paper and used a liquid gasket in conjunction with the paper gasket to seal it. On the throttle body there is a metal plate held on with two screws. It is about 2 inches long and about 3/4 inch wide. Underneath is a sealing O ring in a groove. This at some stage must have been removed and stretched to a point where it no longer sealed. So I purchased a new O ring (diameter size 31) the groove for the O-ring is quite unusual in shape and it was hard to get the new O-ring to stay in the groove. So I spayed the groove and O ring with motor liquid contact cement. After a few minutes pushed the O ring into the groove, then held it in place for 10 minutes till the glue had secured the O ring into the groove. Then I replaced the cover plate and securing screws. Upon starting the car finally after many years the engine idled perfect at 800 RPM even when hot with no further surging. After adjusting the throttle body idle screw I then squeezed in a small amount of silicone sealant into the hole on top of it to seal it. If the plastic throttle body screw should loose its indentation due to age and you cannot get a screwdriver to work on it. Very carefully drill a hole in the centre of the plastic screw, then with an "Easy Out" tool unscrew the throttle body screw out of its hole. Then carefully take a stainless steel screw and with super glue secure it to the hole in the centre of the plastic screw. Once dry and set carefully re-screw it back into the throttle body and adjust the idle speed to 800 RPM. There is a small O ring on this screw to seal it, so if there is any possibility of this O ring leaking just squeeze in a small amount of silicone sealant into the hole on top of it to seal it. Final conclusion from my own experience is that the throttle body has to be a sealed unit with no air leaks. Another problem from when I first bought the car second hand is it was hesitant when cold. This meant first thing when starting to drive onto the highway the engine revs and power would die and I would have to pull of the road and let the car idle for 10 minutes before I could drive away smoothly with full power. Once again none of the experts could fix it, so after some experimentation after removing the sensor wire off the engine manifold down on the front lower part of the motor the engine ran smooth and with full power and revs. So upon removing the sensor I found that at some stage someone had removed the sensor to probably clean or service it and then refitted it using red automotive heat silicon. Big mistake, never use ordinary silicon in the area of engine sensors as the acetone in the silicone permanently damages the sensor. The correct sealant to use is termed Silver Silicone and contains no acetone. Anyway after fitting a new sensor it fixed the problem.

12 out of 12 people think this is helpful.

you could have a cracked boot from air box to intake manifold vary common

1 out of 1 people think this is helpful.
Daniel Foster

sounds like an IACV to me (idle air control valve)


i have the same problem and i have low idling when its cold 200rpm and high idling when its hot....and after 20minutes check engine light off and everything is back to normal...what can i do.....

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