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Discussion Starter · #1 ·
2003 1.8 AWM Tip

I am having a intermittent engine miss or stumble or shutter whatever you want to call it at idle when in gear, warm engine.

No Cel........it happens every 45 sec to 90 secs

Coils, plugs or both??
 

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I've been tracking one down in my car too. Areas to address: cam position sensor, coil packs, fuel filter, spark plugs, cleaning MAF and the MAP sensors. Also, carefully inspect the injector wiring harness. (I cleaned up the ends of the ground wires as they were a bit sketchy looking, though that made no difference).

Mine's always had what I call a rolling stumble in the idle. It got more significant last week or the week before with a definite miss and a p0304 code for a misfire on cylinder 4. I swapped the #4 coil pack for #1, but it wouldn't throw another code after 2 days of city driving so I ordered a single coil pack, which fixed the misfire, so I then ordered and replaced the other three. That made a huge difference in how smoothly the engine ran and the power came on, but didn't fix that rolling stumble. New plugs helped another bit too and after reading the old plugs, I'm convinced at this point that my #3 cylinder is running a tad lean so my next step is to pull my injectors and have them refurbished and tested locally. I ran a bottle of Redline fuel system cleaner through early this winter and that helped just a tiny little bit too. I've got another bottle sitting in my garage but I've also got some cheap Canadian Tire fuel system cleaner in the 1/2 tank I've got now and I don't want to over do it so I'll wait a bit for the next treatment.

If none of that works, you might want to look at the viscous fan clutch: I've read here on the forums that that can cause a faint rumble in the idle, though I have no idea how to tell if that's on its way out or not.
 

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300 rpm? That's an order of magnitude worse than what I thought from what I read in your description coupled with what I'm experiencing. Something that major (from 850 rpm to 600) would throw a code, id'a thunk. Nevertheless, those areas I mentioned are still things to look at. Hopefully more experienced members will jump in pronto.

Edit: BTW... I don't see anything like a 300 rpm drop when my compressor kicks in, more like 20 or 30.... and probably less. I'd go try it right now, but it's -20... not even sure my A/C would run....
 

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Check for major vacuum leaks, they can cause that stalling sensation without any codes. Check the suction jet pump behind the intake manifold as well, those can pop in half causing harsh idles and stalling. Also, try disconnecting the MAF and see if the car runs better with it unplugged. Other than that, I'd clean and align the throttle body to see if that helps.
 

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Discussion Starter · #7 ·
Checked for vacuum leaks and found none. All hoses look new . No hisses, used carb spray and found nothing. It idles fine, it just has that stumble in it just for a split second. You can feel the stumble while behind the wheel pretty good. I`ll have my indy take a look at it this week if he is not to busy.
I doubt I purchase another VW again.........
 

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I have a similar issue with my '98 AEB stick shift Passat. Background data: one owner, 166,000 miles, complete timing belt service 5 months ago, new spark plugs 22,000 miles ago, new MAF about 16 months ago, ICM about 6 years ago, coolant temp sensor about 7 year ago, oil pressure sender and Mobil 1 (VW502 spec) and oversized WIX oil filter almost 2 months ago.

I first experienced the sudden idle drop about a mile after coming off the freeway while stopped, in neutral, at a signal. A sudden single drop of a couple of hundred rpm at idle and then recovery. No CEL or other warning lights. Coolant temp steady 190. Car ran fine after that for another 30 minutes or so and then repeated the same thing. I did an underhood scan looking for visible issues and found a check valve in the evaporative emissions piping that looked pretty sad so I ordered a new one. Other than these 2 blips, the car idles smoothly and steady with the tach needle hovering between 850 and 900 rpm. The next day wife was driving and she noticed the sudden drop and recovery in idle speed. While on the same trip the oil pressure light started flashing and the beeping started. She immediately pulled over and called me. I arrived and checked the oil level which was full and clean...oil and filter changed about 500 miles ago as part of the oil pressure sender replacement necessitated by a sudden oil hemmorhage in the driveway. I started the car and no oil light or beeping, smooth and steady idle no abnormal sounds from engine. I took the car and drove surface streets home with one eye on the instrument cluster. Car ran fine all the way home. I decided to keep driving it around the neighborhood and after an extended drive I returned home only to have the oil light and buzzer come as I entered the driveway. I quickly popped the hood and looked and listened for anything obvious. Nothing, the engine ran smooth and steady and no noises other than the damn buzzer. I decided to swap out the old oil pressure sender with new copper washers and install the new check valve that had arrived. I then drove the car extensively with no issues whatsoever. Today while the wife was driving she noticed the idle stumble again. I drove it around for a while and the idle remained steady an smooth at around 850-900 rpm. Oil pressure light not coming on today.

With this background, any ideas? My son who wrenches for Lexus suggested that something is on the way out and is failing intermittently right now. He further suggested that the coolant temp sensor as a logical failure point. Though throwing parts at the car may end up fixing it, I prefer to try diagnosis first. Any of this sound familiar? Thanks in advance for any insight.
 

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Discussion Starter · #9 ·
Car started "bucking" bad.......Pulled coil packs to change plugs and cyl #3 plug well was full of oil. Changed VC gaskets and plugs all seems fine for now....

would that oil damage the coil pack??

It amazed me that the CEL never cam on.......
 
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