View Full Version : ...pulling hair out of my head... I just don't get it!!

04-06-2011, 06:21 PM
Hello all... I need any suggestions, comments.... ANYTHING!!!
98 1.8t stock engine, with few bolt ons. Running tapp 760cc file, bosche maf, gt3071.

Here we go!!
I gave my car to my brother to learn how to drive and then take it to school as his main commuter.

Car ran fine, never any problems.
He put gas in at a common drinking hole... Two days later, he noticed something strange.
I checke it out and I noticed misfires. Not at idle but while revving.
Troubleshooted, and finally I changed sparkplugs for another set I had. It fixed issue , but problem return after a day.
Basically, the car under load, will misfire on different cyl.
So I have tried, swapping coils, plugs, ICM... Nothing!
Went ahead, and upgraded to the ATW ignition , with rev E coils, did all the wiring...
Car now idles a bit better, and still has hesitation as I rev. When it hesitates , on the AFR gauge shows lean... As it corrects itself it will start to rev up as normal.
I hear intake back firing... If that makes any sense.
I have checked for leaks, swapped throttle body, changed plugs again, capped at 25.
Checked all maf numbers on vag com. I get no DTC other then a simple misfires as I try to rev it and it leans out.
Ecu with new map , still no help.
I'm running out of ideas!


04-06-2011, 06:54 PM
Just to throw this out there, can it be wrong gas? Maybe he put regular in it? I don't know im kinda guessing.

04-06-2011, 06:58 PM
It could be... I did ask him to put in93.
Whether or not the attendant did, is another question.
Or could it be bad gas?

04-06-2011, 07:00 PM
I don't think it is bad gas due to the turn over rate at gas stations. The only way i can see gas going bad would be if it sits. If you have the receipt for you fill up, do the math and see what you payed per gallon to see if you got the right stuff.

04-06-2011, 07:16 PM
Regular gas would cause issues?... I thought u would notice it if you are under serious load... High boost!

Thanks for the suggestion... I
Gonna put in a few gallons of 93 and some drygas ... Try that next!

04-06-2011, 07:18 PM
Im sure regular would, also adding some 93 and dry gas can make things any worse, so go for it.

04-06-2011, 07:23 PM
87 wouldnt cause you issues like this at idle.. without boost our motors are nothing close to requiring high octane.. infact it has a 91 min on the gas door.. when i go on highway trips, i put in 89 as its burned out in a couple of hours and i wont see boost must, if at all. So its def not the gas if revving is causing a hesitation.

Bad gas is a possibility.. as the drums get empty, they have water from condensation in them. Hard to say.

04-06-2011, 07:26 PM
He tried to save money with el cheapo gas!?
Drain it out and fill it with high octane.

If the octane level is too low with a high compression engine, the sensor will sense knock, so the ECU will adjust the timing as such. But an aggressively advanced timing will not see the mixture dense enough to be able to spark the fuel or the flame will be too slow.

04-06-2011, 07:44 PM
This MIGHT be a reason, some gaz station owners are too cheap to remove water that accumulates in the reservoir.
If its a low traffic gaz station, the pump could have fed some water into your gaz tank.
I would try changing the fuel.

04-06-2011, 07:55 PM
I'm definitely looking that route next.. Well tomorrow!

Draining the tank, run it until no
More in the lines and fill it with fresh 93...

Again... The car idles fine... As soon as I give it gas... While in neutral, I get hesitation and the car runs lean according to the gauge.
Also hear intake noise, like a back fire from the intake .

While on the street, I'm not able to get it going because as it build rev, it starts to back fire from the intake , some from the exhaust.. and hesitates. Eventually rpm climbs but not a smooth run!
Car leans out.

04-07-2011, 01:10 PM
vacuum leak(s)? believe it or not, your car is 13 years old (time flies when you're bolting on goodies ;) and could have some vacuum lines that have seen better days that seal shut while idling (more vacuum) and your car runs fine, but while under load, any weak spots or cracks in the lines may cause misfires.. I'd say check those over thoroughly before throwing anymore parts at it..

Just throwin' it out there....

04-07-2011, 05:41 PM
I checked again ... No leaks.
What's causing the misfires is when it starts to lean out. I know it's leaning because I simply see the afr gauge completely drop over 19 : 1.

Now this happens when I punch it or throttle it in neutral.
When I am able to raise the rpm... Above 3k and punch it from there to red line, the more reacts normal.
I only notice it when I'm idling and try to raise the rpm , that's when it starts to lean. Eventually it catches itself and starts to enrich itself.
If I bounce on the throttle. It will rev up normal without any problem. Again, in neutral. Not moving.

Here is a theory.... Let me know what you guys think... Because I'm running out of ideas...
If the cam tensioner is weak or failing... Oil pressure is normal , the chain will have some play. Now, will this play cause the engine to be out of timing and cause it to lean out?
The engine is a bit louder then normal, not like a diesel, but I do hear more noises coming from the rear of the head.

I'm just wondering if this would cause the engine to lean, and eventually build up enough oil pressure to stiffen the chain and rev the rest of the way normally.

Thanks guys,


04-07-2011, 08:31 PM
CHeck out your fuel filter too this can cause lean outs on acceleration but is fine at idle