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zrwon

Intermittent Rough Idle

13 posts in this topic

I noticed my cluster was going dim when idling for more than 2 minutes and would come back up normal, it was the same feeling as when I start the car and then the alternator kicks in, Battery was 6 years old, so I thought that might be it but the new battery didn't make a difference.It runs good when in motion, starts good and idle just fine but when it gets warm and I hit slow traffic, if I sit idling, the idle goes down for 2-3 sec., I think the intercooler fan is on when this happens.A few times I thought it was going to stall.I'm at 97,000 km and never had any problems with it yet. I bought a bottle of Lucas fuel conditionner/injector cleaner for gas and diesel, I know it probably won't cure my problem but I know it is good to do that once in a while.I never replaced the fuel filter but as I said, it runs fine all the time except when idling for a more than 2 minutes but it's not all the time and it seems more obvious when hot, at idle only.

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Start with the basics,Change the air filter, change the fuel filter, (I posted a Technical Wiki in the Articles section) use the fuel additive at every fill up and see if the problem cures itself in a couple of weeks.Canman

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If you have an scan gauge check your battery voltage (even with an normal meter). My alternator regulator went bad and I had the same symptoms. Car off: 12.4 volts (give or take)Car on: 13-14 volts

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If you have an scan gauge check your battery voltage (even with an normal meter). My alternator regulator went bad and I had the same symptoms. Car off: 12.4 volts (give or take)Car on: 13-14 volts

Thanks, I will check that, I needed those numbers, I suspect it might be the alternator because it always feels like when the alternator kicks in after start up and then cuts out and comes back on again.I'm thinking it will eventually get worse and may ruin my new battery if I let it go for too long.

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The dash light brighten noticeably and the fan speeds up when the alternator kicks in after start-up. That would reverse if the alternator is going bad.Possibly entirely un-related, but I've had a surging idle a few times, from about 700-900 RPM. Only for a few minutes, only after a warm start. Never got worse, never stayed for more than a day or two, never caused me more than idle concern, never did more than ask Eddy if he knew of it. (He didn't, maybe injector was his vague guess, wait and see.)

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Posted (edited) · Report post

The dash light brighten noticeably and the fan speeds up when the alternator kicks in after start-up. That would reverse if the alternator is going bad.Possibly entirely un-related, but I've had a surging idle a few times, from about 700-900 RPM. Only for a few minutes, only after a warm start. Never got worse, never stayed for more than a day or two, never caused me more than idle concern, never did more than ask Eddy if he knew of it. (He didn't, maybe injector was his vague guess, wait and see.)

I should add, it only does this after the car reaches the 3 bubbles on the temp gauge, I read my previous post and I mention it does like at start up when the alternator kicks in and then it cuts back out again but didn't specify only when the car is at operating temperature not when cold.When it does that it is at idle for almost a minute and it cycles 2 seconds normal, 2 seconds it goes down, 2 seconds normal and 2 seconds down and when it is down it feels as if there was water in the fuel going through and then back to clean fuel, if the alternator would do that, I would think it would have got worse by now, it's been acting like this for over 2 months now.I will change the oil and all the filters this weekend and hopefully that will fix the problem, if not, I will have to rebuild the alternator and hopefully I will eventually find the problem, on the bright side, I'm never in traffic and why it doesn't bother me too much, I usually notice it when I pull in my garage and let it idle for a minute before shutting it off.I should mention, changing the battery as usual, put the radio in safe mode, I thought it would be as simple as giving my VIN to the dealer, turns out they had to email MB since the guy in service couldn't find my code he transferred me to parts and he said he would have to email MB and call me back, well they can't help me without the radio S/N, so he said I had to pull the radio to get the S/N on the back of it.I bought the car new, so I assume I must have that code somewhere, anyone know where it should be? owner manual? or is it a separate card in the manual pouch? I tried to find my manual but it's not in the car, I guess I'll have to find it if that's where the code is??? Edited by zrwon

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The radio code should be on a small card.

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Posted (edited) · Report post

Honestly check your voltage on the car, running and off. I'll take a video of mine tomorrow once I'm done training, and its exactly what you described.I havent repaired mine yet since its the winter car (no rush). Basically it runs good then revs up to run the alternator. Your going to find your voltage is all over the place and it revs up trying to keep the battery/car at 12v. I diagnosed it as a bad regulator/alternator since I replaced basically anything else it could of been (abs rings, battery, grounds, fuel filter, oil change).

Edited by dmoonen

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Posted (edited) · Report post

Mine was doing this for over a month (1,000km+-)before the alternator couldn't charge the battery enough to actually run the car and slowly killing the battery. Replaced the battery and same thing, the full time I knew it was something going on with the charging system so I had my gauges all setup for the voltage and that is what told the tale.

Edited by dmoonen

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The radio code should be on a small card.

See this thread for more info on radio codes.

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Mine was doing this for over a month (1,000km+-)before the alternator couldn't charge the battery enough to actually run the car and slowly killing the battery. Replaced the battery and same thing, the full time I knew it was something going on with the charging system so I had my gauges all setup for the voltage and that is what told the tale.

You were right, my alternator went, I now have to recharge my battery every night before driving to work the next day, it stopped charging last week but I didn't have time to replace it yet.Now I'm trying to find the thread on the alternator replacement.

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