98 Turbo miss at idle - PeachParts Mercedes-Benz Forum

mdisav · #1 09-08-2007, 07:35 PM

This is a weird one. Car is fine when cold. When it gets warm it misses at idle only in park or neutral. When I put it in drive or reverse it idles smooth.

I replaced all the fuel lines and o-rings. The car has excellent power and pulls without missing when flooring it.

I am thinking one or both of the fluid motor mounts went bad and is not keeping the idle steady. When I put it in drive, is the fluid in the torque converter dampening the motor?

I also cracked the fuel lines at each injector. Each one actually made it idle a bit steadier. So I did not see a particular problem with any one cylinder.

Any ideas or agreements with the motor mount theory? There is no vibration as if the mounts are bad. Just the missing shake.

TMAllison · #2 09-08-2007, 08:42 PM

You've got a dead AC post on Tech forum. Are you certain the stumble is not caused by your compressor attempting to engage and failing?

I would cocentrate on the AC first and if when it is repaired if the stumble is still present look for a minor leak somewhere.

I dont see how the TC can damp engine vibration. You can test your MM by measuring them. There are two rims/rings at the top of each. The measurement from upper to lower rim should be between 17-13mm. Easiest way to measure is by feel using a 13mm bolt head or a socket who's outside dia fits inside your 13mm snugly. You can also lift the engine 1/4" and look down on them with a bright light and look for cracks. Dont lift more than 1/4" or YOU will crack them. If they've never been changed you might justt want to do them anyway. Makes a big difference.

mdisav · #3 09-08-2007, 08:47 PM

The compressor is not even trying to engage. It spins freely and I think it is ok.

It seems like air in the lines and I see air in the lines but I replaced them all and it does not do it at full throttle.

And it is only when it is warm. It does not do it at all when cold even though I see some air in the lines.

aklim · #4 09-08-2007, 08:48 PM

Dirty injectors maybe? How many miles on the injectors?

mdisav · #5 09-08-2007, 08:51 PM

Diesel purge would be good idea but why only when warm. And no change when I crack the injector lines?

mdisav · #6 09-08-2007, 08:52 PM

The car has 149k and has been very well maintained. There is no nailing at idle.

TMAllison · #7 09-08-2007, 08:53 PM

If you see air I doubt it is getting in through the inj's.

I'd look elsewhere.

When was the last time you changed the o-ring on the fuel filter bolt? A lot of us have been neglecting that one and getting caught by it recently. Also the oring onthe bango bolt on the IP between it and the block.

mdisav · #8 09-08-2007, 08:58 PM

Both the fuel filter bolt and prefilter o-ring is new. Not the one on the return line between the pump and block because I did not feel like taking off the manifold. Plus that is the return and under pressure. I would think it would leak.

I just see air in the plastic fuel lines but they are brand new. I cracked the injectors to see if it changed the idle or isolated a cylinder.

TMAllison · #9 09-08-2007, 09:00 PM

Did you do the shutoff valve oring too?

*edit* any plumbing or tie-in associated with your WVO system?

mdisav · #10 09-08-2007, 09:03 PM

Good call! I totally forgot about that one. You would think it would drip diesel though which it is not. I had a 96 that had a leaking shut off valve o-ring and idled smooth. Go figure.

I will try that. Where I see air the most is after the prefilter when I pull on the throttle.

TMAllison · #11 09-08-2007, 09:06 PM

Hmmm....try re-sealing the pre-filter again first becaue you are seeing air at the beginning of the feed side. Must be entering there. You can bend the hold down washer a hair to get more pressure and grease both o-rings with silicone grease.

As for the S/O, it does usually leak but fuel typically goes horizontally (to the rear) or out the bottom before you see it on top of the valve. Look with a mirror up underneath it.

aklim · #12 09-08-2007, 09:07 PM

Quote:

Originally Posted by mdisav

Diesel purge would be good idea but why only when warm. And no change when I crack the injector lines?

As far as I am concerned, it is a good snake oil. You will never know for sure if the injectors are clean and functioning properly. Only way to KNOW is to take it out and have it tested. I thought mine were running well at 120K. One dirty one that needed to be disassembled. Found that out during the test we ran with the injectors out. Could something else be broke in the injectors? Snake oil or DP would never tell you

mdisav · #13 09-08-2007, 09:08 PM

I did do the bending trick to keep things down. I will do the silicone grease. I do have a mirror and I will check but no visual drips or smell.

mdisav · #14 09-08-2007, 09:11 PM

I will take out the injectors and have them tested if I need to when all other options with air getting in are exhausted.

nhdoc · #15 09-08-2007, 10:21 PM

Quote:

Originally Posted by mdisav

Good call! I totally forgot about that one. You would think it would drip diesel though which it is not. I had a 96 that had a leaking shut off valve o-ring and idled smooth. Go figure.

I will try that. Where I see air the most is after the prefilter when I pull on the throttle.

Forget everything else until you eliminate the air, PERIOD! Air in the fuel lines can cause a horrible idle in these cars...don't break one thing until you have fixed what you know is wrong. Your injectors are probably fine...there are people with these engines with a lot more miles than you with original injectors who have no trouble with them...fix the air leak and your car will probably be fine.