Various running problems (ABY coupe)

[tomwood_uk]

Hi guys,

Ive had a couple of issues with the motor for a while now, and it's about time to get to the bottom of them!

First off is idle control probelms. The car generally dips to around 500rpm for a split second when pulling up to a junction, and the problem is amplified greatly if I've been giving it some beans prior. If I'm very gentle with the throttle the problem hardly ever occurs. The motor is fitted with an atmospheric BOV which i've read can cause these sorts of issues. What do you guys think? I've removed and thoroughly cleaned the ISV, to no avail.

My second issue is a hesitation under hard acceleration, usually between 2-3000rpm. Sometimes this can result in a very harsh, sudden drop in power- causing the car to jolt fiercely. The issue is especially present when loading up the car in say 4th or 5th gear at WOT. I performed a boost leakage test not so long ago and found no obvios faults. Any ideas?

Many thanks,

Tom

[benntenn67]

Did you get the second issue after you removed and cleaned the ISV ??

[tomwood_uk]

Did you get the second issue after you removed and cleaned the ISV ??

No it was present before and after i did that.

[AndyP]

Not sure about the idle issues but the jolting sounds like it's overboosting and the ECU is cutting the ignition. Is it std or chipped? Do you have a boost gauge and can you pull the fault codes?

[driftin jo]

Firs off get rid of the atmospheric dump and fit a proper recirc valve. This is a mass air flow based system so when you use an atmospheric dump valve it thinks the engine is ingesting the air being dumped and fuels accordingly (floods the engine) for a second or so when you change gear.
Clean the MAF connector, you are getting fuel cut by the sound of it, violent power cut is the result
of the ECU cutting the fuel, most common cause of this is the connector, then a boost leak then the
MAF it's self being dead.

[tomwood_uk]

OK then sounds like the BOV will have to go. As far as I'm aware the ECU chips are std. I've no boost gauge fitted at present but I do have a gauge in the garage i could fit temperarily. Which vac pipe would be best to T in to?

I will clean the connector on the MAF, and idealy I need to pull any fault codes. I had a half arsed attempt to get the blink codes up before but i could't seem to make it work. Could really do with a dummies guide to vagcom, and try it that way.

[tomwood_uk]

Just remembered aswell guys - the car drinks fuel. At the very best (feathering the throttle) I can average 25mpg. Normal driving will return around 18mpg. I'm presuming that's not normal for a standard motor?

[prj]

Dipping to 500 rpm and fuel cut on boost = 100% boost leak.
Fix it. Pressurize the intake using a compressor and spray soap water everywhere and see where it bubbles.

[driftin jo]

It's not 100% boost leak as mine has done fuel cut twice and both times it was the MAF connector, just plugged and unplugged it a few times and it was fine for another year.

[benntenn67]

Just remembered aswell guys - the car drinks fuel. At the very best (feathering the throttle) I can average 25mpg. Normal driving will return around 18mpg. I'm presuming that's not normal for a standard motor?

S2's are thirsty, I only manage 21mpg normal driving - 27mpg taking it easy on the motorway

[tomwood_uk]

Cheers guys. As i mentioned this problem has been with the car since day one, and i have performed a boost leakage test and done the Mark H mod.

[4WheelDrifter]

Dipping to 500 rpm and fuel cut on boost = 100% boost leak.
Fix it. Pressurize the intake using a compressor and spray soap water everywhere and see where it bubbles.

After reading the OP I 100% agree with it being a boost/vacuum leak. Get a recirc DV on there and leak test it properly.

[driftin jo]

Just so you know, my car used to dip the revs and it was the ISV that needed cleaning and
at the same time as this I had boost cut due to the MAF connector and I can assure you I didn't have a boost leak as all my hoses were new roose motorsport ones and were clamped with bolt clamps.

When I had fuel cut I was told it would be a boost leak and after messing around for hours and pressurizing the system to 30 psi and no leaks found anywhere I was pissed off that in the end all I had to do to sort it was unplug the MAF connector clean and it was sorted.

I not saying in this case it isn't a boost leak just that it is not 100% a boost leak ! 100% implies it can't be anything else and I can assure you it can.

The simple fact is it takes no time at all to sort the MAF connector so before you spend hours looking for leaks it would be worth wile checking it as in my case looking for leaks was just wasting my time as there were none.

[prj]

It's not 100% boost leak as mine has done fuel cut twice and both times it was the MAF connector, just plugged and unplugged it a few times and it was fine for another year.

Don't take what I said out of context.
OPs symptoms are a plain old boost or vacuum leak.

MAF connector will throw codes as well, as for it to fuel cut on MAF connector will mean that it went to limp mode due to "MAF Signal too low".

That said, the BOV can also make it go into limp mode due to "MAF Signal too high".
But okay, 99.9% then.

[driftin jo]

yes it did through a code I think it was something like 'Mass air flow signal implausible'