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Hi everyone, new member here. I've been doing a lot of searching for answers to my issue for a few months now and have tried several things to fix it, but I am at a loss and not sure where to go as the next step. I'll try to be as detailed as possible, so please forgive the long post.
2002 ML320, 207K miles, second owner of a dealer serviced vehicle. I do my own mechanic work. A few months ago, the vehicle started idling rough while sitting in drive. Seemed to smooth out when moving, no other issues, no codes. After a while I got a random misfire P0300, so I replaced all the plugs and wires. Plugs were a little burnt, so I figured it was likely overdue. Cleared the code but the rough idle while sitting in drive remained. The misfire got a little worse over the next few days, and I got P0303, P0300, and P0400, so basically EGR and now random as well as cylinder 3 misfires. Replaced the EGR, which was a complete pain in the ***, cleared the codes, and drove it again. Same issue as before, no change.
However over time it has progressively gotten worse, where the vehicle wants to idle so low that it does this new thing, and here is where I will get very specific:
In drive, stopped, whether the temp is hot or cold, it will start at about 900-1000 RPM idle and then slowly move down to 500-600 range, finally making a dip down to about 300-400 before It begins to sputter, then catches itself and goes back up to 500-600. If I put it in neutral and give it a little throttle to keep the idle up, it's fine. But if I don't, after it sputters it has a pronounced misfire that is consistent while driving. It is so bad that I can barely get up a hill. But if I turn off the ignition and start it again, the misfire goes away completely and I'm back to full power until the cycle begins again. I'm currently getting the same P0400, P0300, and P0303 codes I had before replacing all of that stuff, so I'm at a loss.
Unrelated, but during this whole thing the water pump seized so i replaced that, the fan clutch, and the belt.
If any of you have any insight whatsoever on this, I would really appreciate it. I'm starting to lean toward cylinder 3 being the main issue in some way, but the EGR code should be sorted out with a replacement part and it's not. Thank you in advance, everyone!
Hi everyone, new member here. I've been doing a lot of searching for answers to my issue for a few months now and have tried several things to fix it, but I am at a loss and not sure where to go as the next step. I'll try to be as detailed as possible, so please forgive the long post.
2002 ML320, 207K miles, second owner of a dealer serviced vehicle. I do my own mechanic work. A few months ago, the vehicle started idling rough while sitting in drive. Seemed to smooth out when moving, no other issues, no codes. After a while I got a random misfire P0300, so I replaced all the plugs and wires. Plugs were a little burnt, so I figured it was likely overdue. Cleared the code but the rough idle while sitting in drive remained. The misfire got a little worse over the next few days, and I got P0303, P0300, and P0400, so basically EGR and now random as well as cylinder 3 misfires. Replaced the EGR, which was a complete pain in the ***, cleared the codes, and drove it again. Same issue as before, no change.
However over time it has progressively gotten worse, where the vehicle wants to idle so low that it does this new thing, and here is where I will get very specific:
In drive, stopped, whether the temp is hot or cold, it will start at about 900-1000 RPM idle and then slowly move down to 500-600 range, finally making a dip down to about 300-400 before It begins to sputter, then catches itself and goes back up to 500-600. If I put it in neutral and give it a little throttle to keep the idle up, it's fine. But if I don't, after it sputters it has a pronounced misfire that is consistent while driving. It is so bad that I can barely get up a hill. But if I turn off the ignition and start it again, the misfire goes away completely and I'm back to full power until the cycle begins again. I'm currently getting the same P0400, P0300, and P0303 codes I had before replacing all of that stuff, so I'm at a loss.
Unrelated, but during this whole thing the water pump seized so i replaced that, the fan clutch, and the belt.
If any of you have any insight whatsoever on this, I would really appreciate it. I'm starting to lean toward cylinder 3 being the main issue in some way, but the EGR code should be sorted out with a replacement part and it's not. Thank you in advance, everyone!
Welcome Mike,
Dont think its your cats, (no O sensor codes), but I would check them anyways. Maybe use a thermo sensor gun fore and aft of the cats.
MAF? no codes either. Maybe use some crc to clean it out. Disconnect and see how it runs without it connected.
You cleaned the EGR.... what about vacuum leaks (or electric grounding issue). Check ALL the lines for cracks, displacement (these w163s are getting on in age...)
CPS? No codes displaying, but it could be on its way out w/o an error code.
Fuel filter/ pump? - check the F pressure at the schrader valve.
EDIT: forgot to mention - possibly injector 3 also.
AND I assume you swapped out the coils too?
I did not swap out the coils, but that was where my hunch was. I did replace the rubber hoses leading to the EGR because they were trash, so I'm assuming a vacuum leak isn't the case. I haven't checked anything else you've mentioned, but I did think it might have been the cat at first, but with the P0303 being specific I ruled that put and focused on the #3 cylinder. I was worried about low compression on that one, but again, it goes away after a shutting off/on so it seems electrical rather than physical, if that makes sense.
I did not swap out the coils, but that was where my hunch was. I did replace the rubber hoses leading to the EGR because they were trash, so I'm assuming a vacuum leak isn't the case. I haven't checked anything else you've mentioned, but I did think it might have been the cat at first, but with the P0303 being specific I ruled that put and focused on the #3 cylinder. I was worried about low compression on that one, but again, it goes away after a shutting off/on so it seems electrical rather than physical, if that makes sense.
Either way, I really appreciate your response!
Perhaps swap that related coil with another on one of the other banks and test if the code follows.
Check the other vacuum lines too; it maybe time to swap those out too.
Perhaps swap that related coil with another on one of the other banks and test if the code follows.
Check the other vacuum lines too; it maybe time to swap those out too.
Alright, sorry for the long delay but with all the holiday stuff going on (and another car down) it took forever to get to this. I checked all the vacuum lines according to the diagrams I found, and they all seem to be in good shape with no obvious brittleness or cracks. I then swapped the coil with a different one, cleared the codes, and still got the P0303 along with the P0300. However, after feeling how it's running during heavy acceleration (power is way reduced from normal) and struggling to stay running at idle in drive, I really do think one of the cats, or both, on that side is/are done. From what I've read, that would explain that misfire code and also cause the sluggishness, so I think that's probably where this ends. I'm NOT paying someone to do the job, so if I can't get to it relatively easily I may have to cut my losses. I don't think I can justify dumping a couple of grand into a vehicle with 207K on the clock when I only paid $1800 for it in the first place.
Has anyone done this job themselves? I saw a guide that roughly outlined it, and it looks like getting the performance cats for under $100 each is the way to go. I have done exhaust work before so that's not an issue, but the parts have always been easy to reach. I recall reading something about having to remove a crossmember or other part that's in the way to access the cats on the ML, and unfortunately here in Ohio the weather is not conducive to me being outside with very much patience for very long. Again, I do appreciate the replies as you've at least got me pointed in what I think is the right direction!
Well, you can test the cats to see if they are indeed the issue - use a thermal gun and check the temps of the exhaust pipes before and after the cats. DO a search for some youtube videos on this to get a better take on this. Quite easy to test for.
Check front cats with thermal - exit temp should be significantly higher than entrance temps - check rear cats with a rubber mallet for blockage
Frankly from you diagnosis - sure "sounds" at least 50% chance this is MAF - coming to braked stop - engine drops below normal idle - almost "chokes" then catches itself to cycle up above normal idle - drops/almost "chokes" etc.
Also drop 1/2 bottle Stabil Marine Stabilizer (Blue bottle) in the tank while you are working thru this .
Again, I'd like to thank you all for the suggestions. I finally got a chance to get under the car and measure the temps, and I'm about 60-100 degrees colder on the cat output than the input on BOTH sides. So it looks like the cats are the culprit. I did end up grabbing a MAF sensor just in case I was wrong (Bosch OEM), but when I pulled the old one off it still looked good, and the new one only got about 5 miles after installation before the dash lit up again. So with all that being said, I'm going to call around to see if I can get some quotes for cheap exhaust work. Thanks again guys!
Again, I'd like to thank you all for the suggestions. I finally got a chance to get under the car and measure the temps, and I'm about 60-100 degrees colder on the cat output than the input on BOTH sides. So it looks like the cats are the culprit. I did end up grabbing a MAF sensor just in case I was wrong (Bosch OEM), but when I pulled the old one off it still looked good, and the new one only got about 5 miles after installation before the dash lit up again. So with all that being said, I'm going to call around to see if I can get some quotes for cheap exhaust work. Thanks again guys!
Your low RPM at idle would indicate a clogged injector at #3 cylinder. Warm up the eng. and disconnect the elec. connector at cyl #3 and run the eng. for 1 min. and shut off eng.
Then check for code P0460 and or P0462.
If there was a CAT problem codes would immediately be stored. Do not do anything with your CATS until the misfire is fixed.
When you replaced the EGR Valve, did you notice if the tube was clogged?
11-10-2019, 12:16 PM
