2002 VW Beetle (2.0 engine) - rough idling

I have a 2002 VW New Beetle (2.0 engine) with 163,000 miles. As preventative maintenance I recently had the timing belt and related parts changed (second time since car was new) and a tune-up including spark plugs and wires. Since this work, the car idles rough intermittently and the check engine light comes on sporadically. The codes were something about low coolant/ sensor and misfire on coil 2. The original mechanic could not diagnose the problem. The second mechanic replaced the coolant sensor and all seemed fine until the next day when after driving about 1 mile, the check engine light started blinking (maybe 5 or 6 times), the car idled extremely rough and then the light went out. I immediately stopped the car because I have heard you shouldn’t drive with the check engine light blinking. After about 3-5 minutes, the light went out and the idling returned to normal and I drove to work. The car has intermittently continued to idle rough (seemingly when it is very cold outside or raining - may or may not apply). I had the second mechanic check it and no codes were thrown by the check engine light. The mechanic has checked the sensor, thermostat, coils, timing, spark plugs and wires and all are working fine and he can find no problem with the car. Any idea what’s going on?

It would help if you can post the actual error codes like P0123.

P1296 and P0302

P1296 is for the faulty coolant temp sensor. This is a common problem on these engines and replacing the sensor will fix the problem. This should not cause the driveability problems you are describing. Since the sensor has already been replaced you have nothing to worry about.

P0302 is cyl#2 misfire. This is likely due to the new plugs and wires. Either one of the new components is faulty (on the #2 cyl) or it was not installed correctly. This would certainly cause the problems you describe. It should be an easy fix.

The first set of plugs and wires were returned as defective and new ones were installed. Since that installation by the first mechanic, the second mechanic has removed them all, checked them and reinstalled them. The problem persists, but no new codes have been thrown.

You are correct that you shouldn’t keep driving if the light blinks at you - so good call there. It also means that you should persist in getting this sorted out asap, and stop the car again if/when it has one of its “fits.”

The first possibility is what mrbean said - that there was a problem with the new plugs & wires - either a defective part or a problem with installation. Any of these might have been tested, but there is a real difficulty with finding intermittent faults. Things like ignition coils can come & go, and if they are tested when not acting up they may test just fine. Same with plugs & wires.

Here are a couple of things you can do simply by yourself before you go anywhere again. First, pull & jiggle on the spark plug wires - they shouldn’t pull off, but should be very firmly attached. They are sometimes tricky to get fully seated, and someone in a hurry or not fully paying attention might not get them on right. If any pop off easily, reseat them until they “click” - something between a sound & a feel but this lets you know they are seated.

Also, get a spray bottle of water, start the car and mist the plug wires. If the engine stumbles the problem is certainly related to ignition components, and probably the wires.

If that doesn’t get you anywhere, you could pull the # 2 spark plug wire and swap it with another spark plug wire - see if the misfire moves with the plug wire. You can do the same with the #2 plug.

Does this car have a distributor? I will guess not since you didn’t mention it and referred to coils rather than a coil. If it does have a distributor someone should have a close look at that. If not, and the plugs/wires don’t turn a problem I would be betting on you needing a new coil pack (see above about testing for intermittent problems). But someone should be checking all of the wiring just in case something got damaged or dislodged in the midst of all of that work.

It also wouldn’t hurt to check the compression - how many miles are on this car?

Thanks. All of these are good suggestions. Probably not something I can do myself, but I’m sure it’s something my son could help me with. The car has 163,000 miles. I’ve spent over $1,200 so far on repairs, so I’m trying to get as many suggestions as I can before spending more money.

At 163K I would certainly have the compression checked. Since the problem came after the recent tune-up work, it is more likely to stem from something related to that but checking compression is fairly cheap & easy.

After replacing the ignition coil with a new VW part, the idling problem seems fixed. I now have new timing belt and other belts, new water pump, new plugs, new wires, a new coolant sensor and a new ignition coil – all VW parts from the VW dealer. The check engine light was off for about a week but is now on again. I again have the P0302 code which is the misfire code, but have a new code P0411 which according to AutoZone is an incorrect flow in the secondary air injection system. The possible fixes are replacing the (1) air combination valve, (2) air solenoid valve or (3) faulty air pump motor. Any suggestions how I figure out where to go this time? Or is it time to find a new car?