Author Topic: Temporary Engine problems a few minutes after start up  (Read 3779 times)

Offline Kernowkevin

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Last week, a few minutes after driving the car off from cold, the engine of my mk2 Gti lost power with almost immediate effect. The engine did not stall, it just sounded rough, like it was running on less than 4 cylinders. I pulled off the road & kept the engine running. After a minute or so, the sound of the engine returned to normal. I drove off again and the car drove perfectly.

The following day I tried to replicate the problem on my driveway. I started the car and left it ticking over. After about 4 minutes, tickover revs rose to approx 1200 rpm. Again, the engine sounded rough, like it was running on less than 4 cylinders. Over the next minute or so the revs rose & dropped, rose & dropped. When the revs dropped, the car sounded like it was going to stall but it never did. After that minute or so, the car abruptly returned to a normal tickover. At this point the temperature gauge was just about starting to rise off `zero'. I note also that when standing outside the car that the smell suggested it may have been running rich.

Once the tickover returns to normal on my driveway, I've driven the car and its runs just fine

Each day for the last week, I've repeated the above process after starting the car from cold. The results have been consistent. The only variable has been how long before the tickover problems start....anything between 3 minutes and 5 minutes, and how long the tickover problems last for....anything between 30 secs and 1 min 30 secs.

After I've driven the car & leave it for say 1 hour (so that it's still warmish rather than cold), the above problem will replicate itself after about 1 minute 30 seconds but the tickover issue will last for only 10 secs or so.

I'm conscious I've been making a lot of short journeys lately. I've taken the car for a good, hard, high revving run for 20 miles. The engine ran as beautifully as ever but it did not solve the problem.

The car is run on 99 RON fuel, its serviced and maintained without compromise by an excellent mechanic so poor maintenance is not the cause

Sorry to go into so much detail but I suspect that identifying the problem rather that fixing it will be the most time-consuming/ costly issue here.

If anybody has any ideas I'd be grateful for your feedback

Offline oakgreener

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Re: Temporary Engine problems a few minutes after start up
« Reply #1 on: 03 November 2017, 18:01 »
Throttle body switches, broken wires?

Offline Kernowkevin

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Re: Temporary Engine problems a few minutes after start up
« Reply #2 on: 04 November 2017, 14:53 »
Thanks so much for your reply. I'll add your suggestions to the checklist

Offline Kernowkevin

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Re: Temporary Engine problems a few minutes after start up
« Reply #3 on: 17 November 2017, 19:48 »
I've now resolved this problem by replacing the blue coolant temperature sensor 2 pin 20mm (part code : 025906041)

Its also resolved another long term problem which was higher tickover revs in traffic when the engine was hot. It would appear that the sensor had been faulty, to a lesser degree, for quite some time.