Rough Idle
Thread Starter
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Joined: Nov 2004
Posts: 63
Likes: 0
From: Birmingham Alabama
Rough Idle
My 95 A4 LT1 has developed an annoying, rough idle. My mpg are also down from 18 to 13 (my last tank). I have 118k with the original optispark. Could this be a result of carbon buildup on the rotor and cap? I've been contemplating an LTCC setup, but mounting the coils involves some fabrication time, and I've only got weekends b/c it's my only car. Any ideas about the rough idle? The car also takes a while to crank over sometimes, maybe 2-3 seconds. Driving down the road the engine is silky smooth.
Race Director
Joined: Jan 2000
Posts: 16,485
Likes: 25
From: USA. Northern Virginia
Before you do anything that takes $$$, first check your EGR valve 
Put a vacuum gauge on it to see if it holds a vacuum, then disconnect it plug up the vaccuum line and test drive it...if every thing smooooooooths out...you have found the problem in the EGR valve...good luck
Put a vacuum gauge on it to see if it holds a vacuum, then disconnect it plug up the vaccuum line and test drive it...if every thing smooooooooths out...you have found the problem in the EGR valve...good luck
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
if you need a hand to change your opti, let me know. i just changed mine last weekend and it wasnt that hard at all. my motor has an ati balancer so i didnt have to remove it for clearance. if you have the stock balancer i believe you have to remove it to get the opti off, not sure though. but it wasnt bad, had it off in @1/2 hour and mine only had @8000 miles on it and was badly corroded. i sealed the new one with permatex silicone so no water gets in this one, i like to keep my motor clean by washing it every couple weeks. i also have a snap on fuel injector cleaner if you want to try that and see if it helps your idle. it helped my idle the first time i cleaned them. i bought the bottle of cleaner from ford that goes in the machine. it works pretty good.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
check your history error codes. Sounds like O2 sensor(s) may be hosed and reporting back lean condition to your ECM/PCM, which in turn will increase fuel injector duration. Check your codes...check your codes....check your codes!! (u can do this yourself by shorting pin4 to pin12 on your ALDL connector)....
I had very similar problem, went from 18mpg to about 8mpg, and it turned out to be an O2 sensor with a bent pin(thanks to muffler shop when they installed new cats).......
I had very similar problem, went from 18mpg to about 8mpg, and it turned out to be an O2 sensor with a bent pin(thanks to muffler shop when they installed new cats).......
Thread Starter
Advanced
Joined: Nov 2004
Posts: 63
Likes: 0
From: Birmingham Alabama
No codes and the O2 sensors are 2 months old. The EGR valve on the other hand has been on my suspect since I had problems like Mike's but at around 6 mpg and a blackened rear bumper. I could never figure out why recently replaced O2s (within that year) would fail like that, but new O2s fixed it. The old ones had carbon deposits covering the slits in the O2 sensor.
I'll purchase a vacuum hand pump (My dad has mine in Phoenix along with 95% of my tools) and test the EGR tonight.
I'll purchase a vacuum hand pump (My dad has mine in Phoenix along with 95% of my tools) and test the EGR tonight.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Check fuel pressure leak down for a possible leaking injector.
If found, you can have the cleaned & tested by Rich at Cruzinperformance (link on my site) for about $12/injector + shipping.
If found, you can have the cleaned & tested by Rich at Cruzinperformance (link on my site) for about $12/injector + shipping.
Thread Starter
Advanced
Joined: Nov 2004
Posts: 63
Likes: 0
From: Birmingham Alabama
Sorry for the late reply, got preoccupied running away from hurricanes. I checked the injectors, and they didn't leak when I powered up the fuel pump. I don't have a vacuum pump, but I'll try and plug the egr vacuum line and see if it idles ok. It's strange that it idles so poorly because it runs probably stronger than ever. 
Thread Starter
Advanced
Joined: Nov 2004
Posts: 63
Likes: 0
From: Birmingham Alabama
Update- Checked out my opti and it had oil in it, so I replaced it. The car still idles alittle bit rough. The EGR valve tests out ok. Could I just need my valves adjusted or possibly a head job. I had an MG before with a scuffed valve and the thing wouldn't even idle. Any ideas? 
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