Changed timing belt - idle now rough
 

I recently changed the timing belt, cam & crank seals, water pump and thermostat in my GC8. I made sure I followed the instructions to the letter, and the crank and timing marks were perfectly lined up. Since then the car has had a rough idle. Shakes quite a bit in the car when sitting idling. It has not stalled in the 50kms I have put on it since the belt change. Just a rough idle. When I did the timing belt, I noticed that the belt was out one cog (thanks to the dealer servicing) on the exhaust on the drivers side. I corrected this and made sure they were perfectly lined up.

The car revs fine and has no strange knocking noises. A bit of belt noise. It is slightly sluggish, and seems to have a tiny miss before boosting.

The car is stock as a rock. No modifications at all.

Any ideas what is causing and how to fix my lumpy idle?

What ecu are you running ?

So issue is only after timing belt was done?

Post a video with audio if you can
What does it sound like to drive?

My money is on timing belt out a tooth.

I had by the sounds of it the exact same issue, which appeared after a timing belt change.

The motec timing had been thrown out by the change so the crank and cam angle sensors were trying to read at the same time causing a miss at x rpm. It also caused the car to very rough on cold idle.

If this sounds like your issue go speak to Cash and Sean at Allstar Garage and they'll know the fix

I believe the car is running the stock ECU.

Just a slight miss on idle, makes it lumpy, shakes the car a little. Enough to be an irritation.

I tried to reset the ECU but for some reason I do not think it reset. Connected the green to green, black to black, under the steering column. Accelerator flat to floor, then half throttle. Fan was on and off, clicking sound, but "Check Engine" and a couple of other lights stayed on. No flashes, no nothing. Took it for a drive, no flashing "Check Engine". So bugger it if I know what is up.

Could have knocked the cam or crank angle sensors.

I just connected the black to black and I get a constant "Check Engine" flashing light. No code, just constantly slowly flashes.

Any ideas as to where to next?

I would revisit the camshaft timing.
Disregard the white lines on the belt, especially if it's a Dayco belt.
Rotate the engine backwards by enough that you can slowly bring the crank into position in the correct direction and there's no slack in the belt. Then double check the marks.
Is there a chance you damaged a valve when you removed the old belt? Did the cams all spring off in every direction? Did you rotate the crank at all while the belt was off or was the belt removed at TDC rather than the halfway down the bores position? The valves can easily touch each other if you rotate the cams in the wrong dirrection and they have very small stems that bend easily. If they have bent valves they often have a characteristic valve train noise at certain R/min.

[QUOTE=dtrally;783622]I would revisit the camshaft timing.
Disregard the white lines on the belt, especially if it's a Dayco belt.
Rotate the engine backwards by enough that you can slowly bring the crank into position in the correct direction and there's no slack in the belt. Then double check the marks. [/QUOTE]
I checked the belt a ton of times before I bolted it back together. Turned it over by hand a bunch. Figured how to get it exactly lined up when the tensioner is on. Took me the best part of 2 full days to get it all done. Rotated the crank a ton of times and the marks always lined up perfectly. Even had the better half eyeball it.

[QUOTE=dtrally;783622]
Is there a chance you damaged a valve when you removed the old belt? Did the cams all spring off in every direction?
[/QUOTE]
Sure. There is a chance that a valve is bent. The cams sprung when I took the first belt off. I did however set the crank pulley to the service position before taking the belt off. The crank never moved. I only turned the cams the direction indicated. I am hoping it is not a bent valve as that would be slightly unfair given I painstakingly went through all the steps to the letter, minus not having the tool to stop the cams turning when the belt was first removed. Took me by surprise!

[QUOTE=dtrally;783622]
Did you rotate the crank at all while the belt was off or was the belt removed at TDC rather than the halfway down the bores position?
[/QUOTE]
I made sure it was in the service position prior to removing the belt.

[QUOTE=dtrally;783622]
The valves can easily touch each other if you rotate the cams in the wrong dirrection and they have very small stems that bend easily. If they have bent valves they often have a characteristic valve train noise at certain R/min.[/QUOTE]
I do not have any significant valve train noise. It runs reasonably smoothly. Just that slight miss and shake on idle. It is a bit quieter than before I changed the belt. My better half thinks it is smoother now.

The idle is the thing that is killing me. Just that lump, miss, slightly off. Gives the car a bit of a shake. The engine mounts are mushy as anything so that probably does not help. That said the car has done a cheery 230,000... was hoping to get it to 330,000

Edit: I should also note that it had a slight miss and shake on idle before doing the timing belt. It is now just a bunch worse. I wonder if the retarding of the left side exhaust cam by a tooth (as it was set previously) was deliberate to reduce this miss?

Retarding the cam timing to reduce a miss is not a procedure I'm familiar with, it may be a technique used though??

It sounds like you covered all bases with the belt change. When the cams spring around they only ever close the valves, there's no chance of damage then, only when re-opening them to set the cams in the right position can they clash with each other. It sounds like you were careful in regard to that.

Did you use the upper engine cleaner at the same time? Clean the throttle body and/or change fuel filter?