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Engine Chugging in the Rain

Please help!

I have a 2002 Volkswagon Jetta. It is a great car, but since it rolled over the 100K mark, I have been having some problems with it.

The most mystifying is that I have a “service engine” light that keeps coming on. This is accompanied by a chugging action when I turn the car on in the morning, BUT ONLY IN THE RAIN. It does not chug when it is cold. It does not chug in the afternoons. Only in the mornings. Only if it has been raining.

So, I brought it to my trusty Volkswagon shop. These guys kept an old Rabbit I used to have in running order, long, long past its prime. They did some investigating, tinkered a bit, replaced an oil filter, and nothing. The problem persisted. The light came back on.

I took it to another mechanic. He gave me a full, and costly, routine tune-up. The light went on for awhile, and then…

So, I brought it to my trusty guys again. They admitted, they were downright stumped. They replaced the wires that connect to my spark plugs.

Then, about a week later, I got a new battery.

Everything was going well until this morning (about a week and a half since the new battery). It had been raining all night. I started the car with trepidation. And…NO CHUGGING! Hooray! But, by the time I got to work, the stupid light had come back on!

Why? Help Click! Help Clack!

I am going broke. I am often late for work. I am feeling sad inside.

What is wrong with my VW?

We are going to ask like we always ask,what codes both current and history are associated with the “check engine” light?

Was any defect noted in either the battery,plug wires?

Itemize the “costly tune up” Do you think the provider of the “costly tune-up” should be fixing the “check engine” light at his own expense? maybe yes,maybe no

The codes seem to indicate several misfires at once. They also include a catalytic converter code, which my mechanic told me may relate to gas in the line from the misfires. He said this would be consistent with problems relating to letting my gas get very low, but this has not happened.
The tune up was apparently very typical and included spark plugs, etc, which needed replacing at this mileage anyway, so he is not likely to fix the “check engine” problem at his expense.

Check engine lights are not mystifying. There is a computer that controls & monitors a bunch of the car’s vital systems. When it detects a problem it turns on that little light. As oldschool said this is the first thing that someone should know about to help with your problem. Since the codes have presumably been scanned twice now you could check your receipt or ask at the shops to see if you can get the exact codes. If not, many large auto parts stores will read them for free. You can have that done and post them here - but post the actual codes (like P0301 or something) not what anyone says about them. Based on your description I am going to guess that at least one of these was a P0300 - which is a random/multiple cylinder misfire. But real codes are always much better than guesses. (There will at least be one other for the cat conv).

Anyway…it really looks to me like you need a mechanic that is actually willing to try to address your problem. “trusty” or not it is hard to see how you brought your car to the Volkswagen shop with a misfire and they ended up replacing an oil filter. That’s like washing your hands if your hair gets dirty.

Codes or not it is obvious that you have some problem in the ignition system and that it is related to moisture. This is not so hard to figure out - which is why you really need a new shop. Since the plugs & wires have just been replaced it is time to move farther into the ignition system - to check either the distributor and coil if it has one, or the coil pack if not. The smart money for starters would be problems there with the wiring - loose connections, cracks, breaks, etc. These are the things likely to cause problems when wet.

Must get those codes,espically the current ones. I am having a hard time with the rain factor,usually this would indicate a spark plug wire breakdown,but now they are new. You can have someone spray water around the wires looking for arching but we are dealing with new ignition components now.

In this case first things first,compression check,should have been done by tune-up mechanic. Verify no vacuum leaks and correct fuel pressure at all times.

You will need to verify that the car is not running to lean or rich usually this is done with a VW scanner (VAGCOM) and at the same time we can see if 02 sensors are operating correctly.

This can turn into a fuel injector replacement situation but I will stop now,and start again when you get back with codes.

Since plugs and wires were replaced then my suspects would be, and I’m strictly guesing here a bit, is either moisture affecting a coil pack or moisture is affecting a crank sensor.

Keep in mind that allowing spark plugs to remain in place for a long time can affect the plug wires and can also affect the coils. It’s like dominos; one topples everything in line.
Plug harms the plug wire which harms the coil. Replace the plug and/or wire and the damaged coil may then allow the new plug and wire to fail sooner. It’s a vicious cycle.

That’s my best guess without knowing what codes are present and based strictly on the “several misfires indicated code(s)”

Just for hoots, the next time rain is in the forecast raise the hood and spray in the ignition coils down with WD-40 (engine not running of course). See if the problem goes away…