timetravel

I posted this on az, but I know this is a great forum and hope I can get some help here as well:
2003 A4 1.8t with basic revo software here.

The car had been backfiring occasionally under heavier loads, and fuel mileage was dropping. I had pulled the plugs, which were worn to point, and replaced them with NGK BKR6E coppers gapped to .028. All seemed well for 3-4 days, so I'm unsure if this is related, but I accelerated to pass someone and it felt like the engine missed but the power never came back. Of course this is just as I was entering the highway, and assumed it was a coil. The car drove fine when barely on throttle, but as I applied more gas, it would definitely shake. Frankly, it felt like I was driving on 3 cylinders.

I went and swapped in one revision R coilpack, and passed it down the cylinders, but there was no improvement. While running, as I'd pull the coils, the engine would indeed slightly change tones and vibrations. However, I did notice that the revision R pack would visibly continue sparking as I pulled it off of the plugs, but the other coils do not do that. But I can't be running on one cylinder, so perhaps its a design difference in the R coil, or its a sign that the other 3 are crapping out. But they'd at least have to be working, as I wouldn't be able to fire up or even idle on one cylinder alone. I also pulled the plugs again and checked the NGK's. They were all intact, but appeared to have some carbon buildup on them (only a few days old).

So out came the vag-com, and indeed there were codes, but I couldn't say how long they've been in there.

In "Engine" I had three codes:
16487 - Mass Air Flow Sensor: Signal too high.
With my fingers crossed, I went and bought a new MAF instead of trying to clean what I assumed might be a toast MAF.
18010 - Power Supply Terminal: Voltage too low
Alright, I unplugged the battery
19537 - Engine Temperature too low - Implausible signal
Engine temp sensor?? No idea what to make of this one

and then in "ABS Brakes" I had three codes:
01826 - Sensor for Steering Angle - Intermittent
00526 - Brake Light Switch-F - Implausible Signal - Intermittent
18265 - Load Signal: Error Message from ECU - Intermittent
I don't know what to make of any of these. Parking brake light is not on, but it has flashed and beeped at me in the past.

No codes for any specific cylinder. So after replacing the MAF and putting in a new air filter (btw, who designed that airbox setup??), I gave the car another run. Still not running correctly, but I did notice that the car drives fairly normal on little to no throttle, but as soon as I push the pedal in more than a quarter of the way, the car totally bogs and refuses to rev higher. If I put the clutch in, I can rev freely, although at higher rpms the engine stutters a little. However, as soon as I engage the clutch, the car just wants to limp.

Before, when i first had problems, I was able to accelerate without issue, aside from vibration, and the car sounded like VW's 2.5L 5 cylinder. Now I can hardly accelerate at all. After this last drive, the issue seems to be more boost related. A quick scan, and of course no codes to be found.

Any ideas? I was thinking N75 or diverter valve. Also still slightly stuck on the coils, and considering replacing them all. I thought perhaps the ICM, but I'd have a code. It could be a fuel delivery problem, injectors, rail, pump, filter

Thanks for any input

JAFO

i think i'd replace the engine temp sensor first.

k1.8t

look for boost leaks

warrantysucks

it definatly doesn't sound like a coil issue, if it was your have misfire faults. if you still have the old style black ect (temp sensor) you definatly need to replace it. The load signal you found is related to the maff. the maff sends the load signal to the ecm. take the vag com and look at mvb 3 in engine while doing a pull in second gear. read the block that says g/s. at idle you should read somewhere around 3.5g/s. at a full pull you should be somewhere in the mid to high 100's. like 140g/s

timetravel

thanks man. I actually can't (couldn't) pull any datalogs though because the car won't power through the rpm range. I sent it to RennArt in arlington Heights, IL and their current diagnosis is a clogged cat. An exhaust restriction would certainly explain a lot of this. I'll keep my fingers crossed that they ID'ed it correctly.

timetravel

Scratch that, wasn't the cat, back to the drawing board

diagnosticator1

throttle opening angles, is classic coilpack failure. Due to spark blow out from weak secondary voltage, and the increasing voltage reaquired as cylinder pressure increases with throttle valve opening angle. Recommed you replace all coils with the R version.

warrantysucks

i've seen a couple cases where an injector would stick wide open and just poor fuel into the cylinder, chances of this being the cause is definatly slim. Just food for thought.

timetravel

Thanks, will be trying coils next week if fuel repairs don't pan out

timetravel

I took the car to the dealership to have the cat replaced. They decided it wasn't the cat, and I get the impression that they are just wildly taking guesses at the problem, at my pocketbooks expense. If I wasn't moving 2000 miles away on friday I wouldn't with trying things one at a time here at home.

Anyways, the dealer says the car isn't getting enough fuel, they say pump and filter. I argued whether it could be the injectors instead (or as well), but the service writer was pretty confident about their diagnosis. I should know tomorrow whether their hunch was right. If not, anyone want to buy a rough running '03 A4 Avant jk