Classic Audi Technical Mech/Tech Engine » 1990 Audi 100 2.3 NF - 2500 rpm idle!

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Old 31-05-08, 02:51 PM   #1
pimpdriver
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Default 1990 Audi 100 2.3 NF - 2500 rpm idle!

Hello,

The fuel pipes from the metering head to the injectors were rusty and one had split, so I got some replacements.

I got them off a 2.3 cabriolet, with the NG engine, the same except the pipes are slightly shorter, but they fit.

I have just taken it for a test drive, everything is fine, EXCEPT it idles at 2200-2500rpm. Full power is fine, trundling round is fine, just idling is the problem.

I replaced all four seals on the injectors and inserts (the plastic bits the injectors go in).

I replaced the inlet manifold gasket when I put it back together (the one between the upper and lower halves of the manifold).

The ISV is clean, and works when I put 12V across it.

Any ideas?
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Old 31-05-08, 03:59 PM   #2
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Quote:
Originally Posted by pimpdriver View Post
I replaced the inlet manifold gasket when I put it back together (the one between the upper and lower halves of the manifold).
Air leak somewhere ? I don't know as it depends on the particular engine. On the jaguar AJ engine, an air leak causes a high idle, but on the BMW m20 engine, it causes a lower than normal idle / stalling . Worth checking though.
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Old 31-05-08, 06:08 PM   #3
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it is most likely an air leak somewhere. I could take the manifold off, and refit with some "instant gasket" as well as the normal gasket, there is a HUUUUUUUGE vacuum being pulled in there......... At least the fuelling system works normally, that is what I was worried about.

Halfrauds sell instant gasket type stuff don't they.

Stebe
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Old 31-05-08, 08:48 PM   #4
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Hi PimpDriver,

Sounds like an air leak; If you spray something around the areas you were working you should find the leak.

Spray what??.... doesn't matter much; anything in an aerosol! If it is flammable, the idle will go up when it is drawn in; If it isn't flammable, the idle should drop as it does in 'cos it won't have as much oxygen as the air!

Just chose summat which doesn't harm rubber and doesn't make too much of a mess.

AlanB
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Old 31-05-08, 09:16 PM   #5
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and I noticed that if I take the oil filler cap off, the idle reduces to 1800 rpm.................

I'll get some "instant gasket" tomorrow and bung it on. THere's only one place it could be, and it is fairly easy to do.
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Old 11-06-08, 07:32 PM   #6
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well, so far no change.

I took the upper inlet manifold off, and used the proper sealant as well as the gasket. No change once it was back together.

It starts fine, then the revs drop to 1800, then after approx 5 seconds the revs rise to approx 2400 (after the thermo time switch has done its business).

I sprayed all round the hoses and injectors with an unlit blowtorch, as well as GT85 (kind of like WD40). No change at all. THe Haynes manual says that a leak in the inlet manifold will give rough running, which mine hasn't got. It has full power when needed.

I have checked the operation of the ISV, however, I suspect it may be the cuplrit. There is nothing else it could be, I checked the throttle butterflies are fully shut when the throttle isn't depressed.

A brand new one is 40 inc P&P off ebay
http://cgi.ebay.co.uk/Idle-Air-Contr...QQcmdZViewItem
the part no is:
034133455B

My part number is:
034133455B (from vagcat.com)

I also have a Audi 100 2.2 turbo sitting in a field, which I could rob the ISV off to check, however the part number is slightly different, what do the differences mean (035 not 034 at the start an F not B at the end???)
035133455F Audi 100 2.2 turbo MC engine code

There is also another ISV on ebay off a 90 20V 7A engine code, similar part no, however it has 034 like mine, but F like the turbo?????

Anybody help or should I just try the one off my turbo to see if it will make any difference???

Cheers,
Steve
034 133 455F Audi 90 20V 7A
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Old 11-06-08, 11:47 PM   #7
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Hi P-D,

If I had the parts sitting there, I would try 'em!......If only for diagnosis, rther than repair.

If you get no change at all, it proves that you are barking up completely the wrong tree.......

AlanB
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Old 12-06-08, 07:13 AM   #8
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Can you clamp the hoses off on the iscv when it starts to fault?

Leastways youll know if thats the possible problem, and best of all its free.

Just had a thought; Some iscv's (Ford for example) have a diode across the terminals which if you apply 12volts to the terminals in the wrong polarity can blow that diode and render the iscv faulty.
I only mention this as its possible you may have introduced a fault having cured the original, with the iscv "problem" masking it now.
Sound like a possible?
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Old 12-06-08, 08:23 AM   #9
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I would think that it might possibly be something to do with the fuel system. Did you disturb the metering head. There may be something lodged in there creating a high idle. Are the new injector seals of the same type as those removed? Do they all seat ok? It is easy to damage the seats when removing them. When re seating them there should be an audiable "pop" as they click back in. You have to give em a good shove.
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Old 12-06-08, 09:39 AM   #10
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Just worked out how to do multiple quotes!

Quote:
Originally Posted by 4v6 View Post
Can you clamp the hoses off on the iscv when it starts to fault?

Leastways youll know if thats the possible problem, and best of all its free.

Just had a thought; Some iscv's (Ford for example) have a diode across the terminals which if you apply 12volts to the terminals in the wrong polarity can blow that diode and render the iscv faulty.
I only mention this as its possible you may have introduced a fault having cured the original, with the iscv "problem" masking it now.
Sound like a possible?
I will try clamping off the hose, by squeezing it with a pair of pliers.

I did put 12V across the ISV / ISCV both ways, so I could have knackered it by doing that.

I will pop up to the farm and nick the one off the 100 turbo, my wife is currently having "labour pains" so may have to go into hospital (again!) today.

Quote:
Originally Posted by Octanejunkie View Post
I would think that it might possibly be something to do with the fuel system. Did you disturb the metering head. There may be something lodged in there creating a high idle. Are the new injector seals of the same type as those removed? Do they all seat ok? It is easy to damage the seats when removing them. When re seating them there should be an audiable "pop" as they click back in. You have to give em a good shove.
Didn't touch the metering head, apart from to connect new pipes. But it does run absolutely fine under load, on both throttle butterflies.

THe new injector seals are identical, I replaced 4 on each injector, as well as the plastic "inserts", I put them in and out a couple of times, and they did "pop" in correctly.

ALso they are retained in the head by the retaining strip.

Cheers,
Steve
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