Hi All

I have begun to notice that my car shudders / idles really rough in reverse and drive (progressively gets worse when idling at traffic lights). Above 1000 rpm it isn't noticeable whatsoever. I really want to nip this in the bud before something serious occurs.

Bit of background car had a service (Oil, Air Filter, Fuel Filter and Spark Plugs) at 120,000 kms it is at about 150 000 right now I replaced the drive belt today as it had split vertically and the battery was changed about 2 months ago as the old one could not hold a charge.

Other issues include really slow driver power window and ticking air con (annoying but manageable)

I bought this car when I was 18 with a full service history (no problems) I am 22 now and other than being extremely thirsty it has been very reliable, only serious problem it has encountered is a broken muffler.

To address this shudder / rough idle I checked my PCV valve to see if it had disintegrated however it was completely intact. I then cleaned the throttle body and used a can of upper engine foam. The car felt much more responsive and smoother after doing this however the rough idle / shudder still lingers at low RPM's.

I would prefer to try anything before taking it to a mechanic and paying $$$$

Any suggestions?

When were the coils last replaced?

Without looking at the service history I can tell you that they have not been replaced since I have owned the car (90k) and it is now at 150k.

What is the easiest way to tell if a coil is dead?

The shudder does not occur when the car is cold, I have read that they tend to fail more when the engine is hot?

So, the shudder occurs:
- When warm, but not when cold. Cold start enrichment adds more fuel, but it leans out as it warms up. This suggest the shudder may be caused by running too lean.
- When in gear, but not when in neutral or park. Putting it in gear increases load (less vacuum) which also changes the fueling.

When was the last time you ran injector cleaner through it? May be worth running a bottle of it in a half tank of 98 octane.

I would check the O2 sensor first. With the engine at operating temp, unplug the sensor (and leave it unplugged), reset the ECU (unplug ECU for 1 min or battery for 30 mins), then take for a drive. This resets the fuel trims and prevents the O2 sensor from changing the fueling. If the problem goes away, your O2 sensor needs replacing. If the problem isn't the O2 sensor, plug it back in after you have finished testing, or you could damage it over time.

It might be a dumb question but has it had a service since 120000k? Oil, oil filter air filter? If not it might just be clogged up