Guys my car has this shake on idle for the last 10,000 km and its doing my head in! I have noticed that in drive it is a lot worse than park. Once the car is running (moving/ driving), feels perfectly fine- no misfire or laggy acceleration and perfect fuel economy.

I took it to mitsu the other day and they said that the 3.5 motor had a rough idle to begin with. Now i doubt that because before i got the timing belt changed and rocket cover gaskets it was running fine, perfect to exact. I noticed that the when i got it back it was running a bit rougher.

Now i have ran injector cleaner through it, changed the oil (with a flush etc). Things that i can think of- monkeys didn't but the engine mount on properly, or the idle motor needs to be reset because they disconnected the battery for some odd reason.

Any ideas or thoughts? 100% sure this occurred after i took it for the service! i cbf taking it back there as its pretty far and i already been back there once as they didn't fit the cam seals properly, not keen on doing business with them.

ISC and the ECU work together to set the correct idling speed, doesn't need to be reset in any way. What is the cold and hot neutral idle speed? Test the ISC by turning the air con on when the engine is hot, you should get a noticeable jump in revs. If not, check that the ISC is actually plugged in, you never know.


If it was my car I would pull the covers off the cam belt, and check for correct alignment on the cams at top dead centre. Just to be sure they put the new belt on correctly.

on cold it sits around 1200rpm and then drops to a stead 800ish, the actual idle doesn't move but the engine shakes.

What is the ISU and where does it plug in?

Idle speed is correct from those numbers, so the ISC (idle speed control) motor is working.

Engine shake can be caused by misfiring on one plug at idle, perhaps check the plugs after some time at idle, the misfiring plug will be darker than the others. If so, try a different plug. If that doesn't help change the spark plug lead.

If that doesn't help do a compression test.

Perhaps give MAF sensor a clean, i had similar issue & it got a lot better after that, its really easy to do all you need is MAF cleaner spray for about $20 from autobarn. Also cleaning throttle body can help.

The battery may be on the way out.

Try another one...we had that issue with our magna once.

So it sounds like you've just had a major service done if you say your timing belt has been changed.. Were the spark plugs changed at the same time? Might just be due for some new plugs as they tend to get a bit rough around idle after a while. Usually due to old plugs in the rear bank.
Maybe just pull them out & have a look to see if one (or more) is dirty? If they haven't been replaced for a while, swap them out & see if that fixes it!

well that is what i will do either tonight or tomorrow, first eliminate the small things :) hopefully the sparkies are the issue.

So what exactly was done, just belt or more

Your injector flush, was it just a bottle of throttle in the tank or a proper injector clean

Unless the belt was not put on correctly, it is not poss to have a bad idle from just belt however if they have damaged a plug lead when they did the rocker cover gaskets this may also account for the ilde.

Also sagged trans mount may be loading the roll stops up and causing you to feel more through the car

ok on day one- rocket cover gasket was changed, car drove perfectly fine- this was changed as an RWC item. i picked up the car drove it around for a few days.
a week later the water pump siezed at 160km so i changed the pump and put a new timing belt kit.
once i got the car back it had a really rough idle so i used the redline fuel system cleaner as a petrol additive to see if it helped- nothing!
a few days ago (10,000 km later since timing belt was changed) i done a complete engine oil flush and still no change.
Took it to mitsu and they reckon that the motor is pretty rough but normal for this type of engine. Now my theory is i might as well get it looked at now rather than keep driving it around as i know that it doesn't feel right! plus the fact that it had no shake before makes me think mitsu is not that wise

. . . . . .the water pump siezed at 160km so i changed the pump and put a new timing belt kit.
once i got the car back it had a really rough idle . . . .
Confusing! You put the new belt on or you paid someone to do it?

Either way, you should check the belt for correct installation.

ok just changed the spark plugs (front only) might have made a slight different but nothing that seems to have fixed the problem! needed to be changed anyways so its alright. looks like i will clean the MAF sensor over the weekend.

Any other ideas gents?

Confusing! You put the new belt on or you paid someone to do it?

Either way, you should check the belt for correct installation.

i got it all done at the same shop. I don't really understand what is there to check? all the markings line up fine- plenty of tension, no leaks from the seals etc....

ok on day one- rocket cover gasket was changed, car drove perfectly fine- this was changed as an RWC item. i picked up the car drove it around for a few days.
a week later the water pump siezed at 160km so i changed the pump and put a new timing belt kit.
once i got the car back it had a really rough idle so i used the redline fuel system cleaner as a petrol additive to see if it helped- nothing!
a few days ago (10,000 km later since timing belt was changed) i done a complete engine oil flush and still no change.
Took it to mitsu and they reckon that the motor is pretty rough but normal for this type of engine. Now my theory is i might as well get it looked at now rather than keep driving it around as i know that it doesn't feel right! plus the fact that it had no shake before makes me think mitsu is not that wise

aren't the timing marks on the rocker cover?

maybe the belt is a tooth out....

Ok, your water pump seized up, did the engine stop, get hot or what alerted you to this

If you want to drop over here, perhaps a comp test may be the first step as when the pump seized up you may have even bent a valve if the belt jumped at all, a comp test will clear this up pretty quickly as will a pressure test if the engine got hot

so the plugs weren't changed mate? i was going to suggest they were changed with the wrong type. have you checked the leads for damage as suggested above?

i have the same problem on my TL at the moment. had a mechanic look at it and within half hour found that the thing that opens and shuts to allow air into the engine (throttle control i think it's called) was jammed open and wouldn't close. drove fine for 100km's but has gone back to the way it was before. i think i'll need to check it out myself, and try cleaning it again - downloading the workshop manual as i type this.

thanks to Elwyn for supplying the link http://www.lisho.net/?page_id=3

Ok, your water pump seized up, did the engine stop, get hot or what alerted you to this

If you want to drop over here, perhaps a comp test may be the first step as when the pump seized up you may have even bent a valve if the belt jumped at all, a comp test will clear this up pretty quickly as will a pressure test if the engine got hot

I turned the car and a really loud squelch came out of the cam covers. I drove the car down the street and noticed the temp gauge move to about 4/5 to hot (about 2min of idle and 10sec of driving), so I took off the cam cover and pump seized. I got car towed to the mechanic and that was the end of that. I doubt that there was any damage done….?

Either way, I would be starting with a comp test, when a pulley stops, all sorts of things can happen at the moment in time, have seen it all before

If is not that, you cannot then blame the workshop if they got the marks lined up, other causes would need to be diagnosed on the car, doing this on the net is very hard, you will end up replaving many of the "usual" things before you find it

I had this problem.

Changed the plugs and that fixed it.

I had this problem.

Changed the plugs and that fixed it.

Was this the all the plugs and leads? or just the fronts