Richard H

Merry Christmas all...

Anyone know what is the best/easiest way to check for vacuum leaks?
Also what syptoms would you get if you have a leak?

Thanks.

Richard 1990 C2

Ade - C4 91

Hi Richard,

My C4 had extensive vacuum leaks when I purchased it.

It exhibited very rough running, was hard to start, had bad idle, but most noticeable was the surging and jerkiness.

I replaced all of the hoses, the Tee union, and the two valves. Note: this area is quite different on the 90 model as P redesigned the intake area esp. the idle control and bypass in 91. But I think its essentially the same. This stuff is cheap and easy to replace.

When my mechanic last worked on the car he also reset these valves. I'm not sure if this was done via DME (Computer) or via some other means, but it did help "Solidify" the feel of the engine.

One thing I noticed is that when the system is holding pressure correctly, if you disconnect the Tee Union, you will get a small hiss when the air is released.

What you haven’t mentioned is what symptoms you are getting! There are so many areas that can cause the same bad behaviour (poor ignition, earth, battery, O2 sensor, temp sensor).

Good luck

Ade.
91 C4

Richard H

Thanks Ade,
The problem I get sometimes is.....
After running for a few miles then stopping and trying to restart it sometimes has difficulty in getting going again. Cold start is perfect and once running idle is rock steady at just over 800. Also hot starting is fine if the car has stood for a while. Sometimes if you put the clutch in and lift off the gas the idle drops low then bounces up to just over 1k a couple of times before settling steady at 800. I've changed the DME relay, checked engine temp sensor (reistance at different temps, okay), idle switch, checked (voltage to) and cleaned Idle control valve e.t.c, e.t.c.. Adrian suggested problem around the air flow sensor i.e. overfill of oil e.t.c. I'm sure I haven't over filled with oil but I did notice in the oil tank breather pipe small amounts of 'yellow gunk' all I can assume this is condensation mixing with oil vapour. The problem is that the car lives outside and doesn't get driven for long distances (school runs e.t.c.) so doesn't get a chance to run at operating temp for decent periods. This has just started as the cold weather has arrived, I've had absolutly no problems at all in the last 1 1/2 years.
My intention is to have a good look and clean of the inlet area over the break and have a decent drive! Just thought The bouncing idle could be to do with the vacuum.

Richard 1990 C2

Adrian

Dear Richard,
Check your dipstick. If the seal is damaged or failed the symptoms you indicate will occur. Check the airbox for security as well. You can use soapy water to search for an air leak around the throttle body,
Ciao,
Adrian
911C4

Richard H

Thanks Adrian,
I removed the air box and airflow sensor today and checked it all out. Couldn't find anything obviously wrong except the bolts bolting the airbox and sensor together were not tight, not loose but didn't require any force to release. Could be as you suggested, a leak? A big potential disaster if one had come loose and gone into the engine!!!!!
I disconnected and reconnected the battery and went for a good drive. Started okay hot after a few minute stop and again after imediately switching off.
Hopefully it's okay now!!!!!

Richard.

Adrian

Dear Richard,
The airflow sensor is a sensitive puppie. Tightening up would have removed any leak around it but more importantly will remove any vibration from the mechanical part. Yes a bolt down the engine is not good,
Ciao,
Adrian
911C4