Classic Audi Technical Mech/Tech Engine » cold start problem - 85' cq

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Old 26-02-17, 07:55 PM   #1
andya
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Default cold start problem - 85' cq

Hi all. From cold only, it starts fine, but the revs jump to 2500 rpm, then flucuates, then when it warms up (can be a few minutes waiting), the revs go back to normal and all is good again.

Any ideas? Its an 1985 KV coupe quattro

Andy
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Old 26-02-17, 08:55 PM   #2
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Does it have an idle stabilisation a la later cars, or an auxiliary air valve like a WR?
I believe it should have the usual cold start injector, too, although this may be irrelevant at this point.

If it's revving high, but otherwise everything is working as it should; idle control/auxilliary air?

Probably of absolutely no help. Sorry.
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Old 27-02-17, 01:24 PM   #3
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KVs have aux air valve.

Try starting it with the AAV disconnected, you'll probably find it's going to idle low until the oil viscosity changes.

I had the opposite. With the AAV connected, it'd run at 2+k rpm even after warming. So I've disconnected mine and set my idle manually by the screw, when warm.

Chris
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Old 27-02-17, 07:16 PM   #4
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Cheers Hoyle and Hanuman! Something to go on......


Thanks again
Andy
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Old 21-03-17, 08:12 AM   #5
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Well to give you an update,

Mine has the idle control valve, not an AAV. I've swapped it over with others, no difference. Other things I've tried

1. Refurbished the Bosch warm up regulator - got it done professionally, made no difference

2. Replaced various hoses - especially the ones that carry oil - that one behind the isv had turned to a floppy mess! Luckily I've just recently broken a kv GT for parts and I've been swapping bits over. As I have no idea on the state of the vacuum pipes to do with the intake (nylon sheath protection, probably 30 years old), I have just ordered some replacement pipe to replace.

3. After taking the air intake box off yesterday, I could suddenly see the overrun solenoid, and the wire had broken off its clip and was overhanging the exhaust manifold - the result was a melted mess and a connection close to breaking. Like I say, ive just broken a GT, so it was a nice easy swap over. Optimistically I thought this might solve it. Nah!

So I am fast running out of ideas. I have 2 more things to explore - changing those vacuum pipes, you never know, there may be a leak.

And secondly what about a fuel pressure problem? The system relies on the pressure in the system until the pump starts. It could be if the pressure is initially too low, it causes an over revving problem. I'm taking the cq down to Cornwall for a week (i can live with this for now!), but will look to pressure test it on my return, I'll also change those vacuum pipes at the same time.

What do people think? Is there anything else I should be looking at?

Many thanks
Andy
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Old 22-03-17, 08:54 AM   #6
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Manky throttle body full of oil and rubber.
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Old 22-03-17, 10:27 AM   #7
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What about temp sensor?
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Old 14-01-18, 08:39 AM   #8
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Update on this one:

The cold start issue has gone on till now, when my new years resolution was to get it sorted! Well it's now fixed!

There was a combination of factors that I reckon somebody may find useful if it ever happens to them. Checked every hose for leaks, replaced every vacuum pipe with brand new silicone hoses. There were leaks, bit it wasn't the main problem. The warm up regulator that I had refurbished - faulty!!! I pressure tested it, and it was at 10 bar under pressure. Replaced it with an old spare oily reg, perfect! So it's stayed on, and now wondering whether I can contact the firm where I had it refurbished and get it sorted - it's just a pain in the arse!!

Last weekend I also set about replacing the throttle body, as the switch on the body itself is broken. That's all sorted. In my quest for air leaks, I found that the fuel injectors were quite loose where they sat in the cylinders - you could wiggle them around, and having no idea when they had been last done, thought this should be my next port of call. So during the last working week I ordered new seals, o rings and inserts from Quattro Corner, and the bits he didn't have from VW Heritage. Yesterday I did the job, including cleaning the injectors in an ultrasonic bath. The spray was so much better afterwards!! All back together again, start from cold, hallelujah!!!!!

Real test is this morning, from cold!

However there is a sting in the tail. All put back together again in the dark last night, I could adjust the mixture, but turning the idle screw made no difference. This reared its head last week. It would indicate an air leak, but I've now covered everything!

Any ideas, got another day today to try and sort
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Last edited by andya; 14-01-18 at 08:48 AM.
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