[donkshophorse]

hi folks, can someone explain these symptoms to me and a possible cause please?

1. from cold, slight engine missfire, with reluctant acceleration. fine after about 5 minutes
2. when warm and sitting at idle the engine still stumbles with a missfire. its subtle but just not right
3. when i operate the engine, to rev it from the engine bay, it goes to limp mode and has to be restarted, then all is fine again - still with a subtle stumble though. am i pypassing some clever piece of electrickery by not using the accelerator peddle?

things i've tried:
1. new distributor caps and rotor arms
2. all leads checked for resistance levels - all fine. checked from distributor cap to spark plug connector, ie the whole cable.
3. spark plugs changed
4. coils changed
5. wiring harness is fine and each injector seems to be pulsing fine (listened to them via stethoscope with my indie)
6. cleared fault codes, nothing else listed (although it did have a MAF reading issue - but it cleared ok)
7. checked fuel pressure - fine, 50psi
8. replaced fuel pressure regulator - this helped as it stopped the car from flooding, which it did in very cold weather.
9. terraclean helped but not cured

the car still pulls fine and has never let me down but i just know this is not right and want to get to the bottom of it. could it be any of the following and how do i check them please?:

1. catalytic convertors
2. a dodgy injector
3. MAF
4. throttle body actuators (not really sure what they are but i am concious of some of you on here saying you had issues with them)
5. faulty engine mounts
6. something else?

thank you in advance for anything you can offer to help.

 

[lcmlee]

My first guess would be fuel quality. If you are not filling it with 91 octane or better then that's your problem. If you are then try a different gas station.

FYI: I have had the same problem before and it was various reasons...the last one was the above mentioned. I had switched to 89 from 91, and the exact description of the issues you are having manifest itself. It even stalled and would not start for 1/2 hour, had to let the car sit. On start up it would hiccup now and then. From idle it would not be smooth. Going back to 91 octane...the W140 has been purring ever since...that was many years ago.

 

[iss]

unplug the MAF sensor and start the car. let it idle for a 30 sec. and go for a short ride ( 5-10min. ), then park it and rev it up few times. Let us know if anything has changed.

 

[donkshophorse]

I use 97ron super unleaded, good idea to try a different station though i do tend to stick with the same one. i'll give it a go.

tried the MAF work as suggested - both MAFs. noted a smoother idle with them disconnected. i'm guessing that means i need new MAF's!!! do i need to change both do you think?

thanks for the info and ideas.

 

[iss]

tried the MAF work as suggested - both MAFs. noted a smoother idle with them disconnected. i'm guessing that means i need new MAF's!!! do i need to change both do you think?

try to clean them with a MAF Sensor Cleaner

 

[donkshophorse]

great minds...

i should have said earlier tried MAF CRC cleaner a few weeks ago, no difference. thanks for the links though