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Car wont rev above 1500 rpm when cold

7K views 22 replies 8 participants last post by  tuttebenne 
#1 ·
Car is a 1994 E420, can't seem to track down this issue.

When the car is at any temp below full OT it will not rev above 1500 rpm. It acts almost like when you hit the rev limiter at the redline kind of goes up to 1500 then drops to 1000, then goes back up etc. Once the car hits OT it abruptly stops having the issue and drives completely normally until it cools down again.

This car loves to get water in it's distributor caps so thats the first thing I checked. They were dry, but I cleaned them out anyways.

Other things I've tried:

  • Unplugged o2 sensor, ran more rich but didnt change the issue.
  • Unplugged MAF, car didnt like that started stumbling but stayed on.
  • Hooked my Vacuum Gauge up, read normal timing and went to 0 when revved.
  • Metered the ecu coolant temp sensor, ohms checked out.
  • Did a smoke test on the vacuum system and didnt see any smoke come out anywhere

Also this car had the engine wiring replaced by the factory under recall, I took a peek at them and they don't appear to be cracked in any way.

I'm not entirely sure if I'm describing what its doing right, so I made a video of it. Maybe that will help:

Video

I'm going to try pulling some codes as well, I made one of the DTC readers but I have yet to actually use it.
 
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#3 ·
Car is non ASR.

The throttle actuator gets confusing, I have the cable running from the pedal onto a linkage that pulls the throttle open with the pedal mechanically, There is a plug for the MAF on the other side of the linkage.

Does my car still have a throttle actuator if I don't have an electric throttle? (Probably a dumb question) and secondly is that plug on the MAF for both the MAF and the actuator if I have one? Or does the Maf in this car need like 8 pins for some reason.

Thanks for the help!
 
#7 ·
Sorry for the late response and bump.

I ran into a string of issues starting at getting the codes from the ECU to post here for your guys and ended up eventually finding the issue. Wanted to update this thread in-case someone has the same issue later, there's actually a solution.

So the first issue I ran into was the fact that I could not retrieve the codes from the computer via the 8-pin connector near the ECU as well as my Impulse Reader. Thinking my impulse reader may have been broken I took the car to an indie that I know to have him hook it up to a multiplexer. The ECU read from there, and everything showed completely normal, except for slightly high spark-plug voltage, there were no codes stored.

---

Fast forward, after checking every fuse (including the 4 hidden ones under the ECU cover) I was at a loss.. that is until I bumped the ETA wiring harness on the top of the engine while checking the throttle linkage and caused the car to stall.

That was confusing, so I cut the sleeve on the harness open a bit to see what was going on in there and what I found was that every single wire in the sleeve had no insulation left on it. I'm talking it was a big bunch of copper in there all touching.

Now that i've "disturbed" it the car won't stay on confirming my suspicion about the throttle causing the issue.

---

I cannot yet confirm 100% that this was truly the issue, but as I do electrical stuff for work including soldering my plan is to take the ETA off the car and rewire it with some nice wire that doesn't have bio-degradable insulation on it and see if I can get that to work. If not I guess its $1000 for a new ETA.


Thanks for the help guys, I'm going to respond to this thread again once I have attempted the rewiring to report if it solved the issue.
 
#11 ·
Thanks for this, I ended up sending the throttle body out to them. They tried 3 harnesses on it and I guess the board fried, so the throttle is not repairable :(


Thanks for posting your results. If it's been stated once, it's been stated a thousand times that the eco junk soy based insulation original is a time bomb.

Have you changed your upper and lower harnesses? If they haven't been upgraded, don't disturb them until you have a replacement in hand. eBay is your friend to find a replacement. You can find post 1997 build date ETA's there for approximately $250 or less.

Good luck

Jayare
I'm currently looking like crazy, I can only find ones with the older style plug, I need the straight one not the sideways one.

check date on main harness

I found a newer date ETA on local CL for less than $200 but I live in LA where clever guys hit the pick'n'pulls looking for good replacement harnesses and ETA
If that thing is still available I'll buy it right now, do you have a link?
 
#9 ·
Thanks for posting your results. If it's been stated once, it's been stated a thousand times that the eco junk soy based insulation original is a time bomb.

Have you changed your upper and lower harnesses? If they haven't been upgraded, don't disturb them until you have a replacement in hand. eBay is your friend to find a replacement. You can find post 1997 build date ETA's there for approximately $250 or less.

Good luck

Jayare
 
#14 ·
Update:

I ended up calling around to different repair shops looking for rebuilt units, I found a guy on ebay that was willing to sell a rebuilt one with a 3 year warranty for $440.

I ended up buying that one, because in my case its pretty hard to locate one with the correct plug on it, sure I could wait around for one to show up, but it probably will be from a junkyard or a used on ebay so it wont have a warranty etc.

Given that the only other offers I found for them was $2500 from the dealer or $1200 through BBA, $440 sounded pretty appealing.

---

That being said who knows if this is going to even solve the problem, if the old one was damaged enough to hurt the throttle who knows what it did to the computer etc, i'm hoping for nothing but the man who expects nothing will never be truly disappointed you know? :p

I destroyed the PCV plastic hosing that connects the throttle to the valve cover in the process of taking it out, as well as the boot that connects the MAF to the throttle so I'm making an order for those today, now that i've sourced a throttle. I also noticed that those plastic vacuum lines hanging around the engine all seem super brittle, I broke one a few months back on the EGR and just sort of clamped some rubber hosing to both ends for the time being. I'm thinking now is a good time to just swap them all while I have the throttle out and have more room in the manifold area.

The throttle should arrive on Friday this week, I'm hoping to have the boot, hose, and vacuum lines in by Thursday/Friday so that hopefully this weekend I can just tackle the whole job and get that poor car running again.

It hasn't been properly running since August of last year and my other car is a 4cyl 4runner. So as you can imagine I'm pretty anxious to get behind a v8 again. I'll post my results once I have the stuff in the car, I may take some pictures as well because prior to taking out the throttle I couldn't find my good guides on it, hopefully that helps some people in the future who are running into similar problems/situations.

Thanks again for all the help!
 
#16 ·
tobolate, don't suppose you're near the SF Bay Area? I just finished discovering bad wiring in my ETA, too. 1995 E420. Exact same symptoms as yours.

Fortunately, I was able to move the ETA harness to a new position and the car is running fine now. I'm making plans to take it out of service to do the wire replacement myself.
 
#19 ·
Well, after weeks of sourcing parts I'm happy to report that the issue has been solved.

The new unit arrived after a few days but unfortunately my local Benz dealer needed to order the MAF boot as well as the PCV breather hoses (from throttle to valve cover) which took another few days.

As you could assume, all of the rubber parts and vacuum lines in the vicinity of the throttle were very brittle and broke upon removing the defective throttle. I ended up just replacing all the vacuum lines in the engine bay as they were all in a similar condition to the ones on the intake manifold, as well as the PCV hoses from the throttle to valve cover because the valve cover end was slightly torn and leaking and I messed up the throttle end of it removing my old one.

Once I had everything back together the car started right up, although a couple strange things happened that I was hoping someone on here could explain.

The "bulb-out" indicator light on the instrument cluster was illuminated after starting the car. Although I confirmed that all exterior and interior lights on the car were working.

The car drove normally, I did a short drive and then let it cool down. About an hour later I went out to try and start it again and it would not start up. Just cranked forever, no spark. It smelled gassy and the fuel rail had pressure so I assumed it had fuel.

---

Undid the battery over night, came back the next morning, car started right up.

This time, there was no bulb indicator light on and I drove the car much farther, about 35 miles.

The engine started acting kind of funny about 15 miles in, kind of like the distributor cap wasn't dry. When I would accelerate it would hesitate and kind of feel like a miss. But within a mile stopped doing that.

---

After that the car has been running completely normally for 2 days. Throttle response is much better, feels like its regained some lost power and the idle is so smooth I can't tell my engine mounts are bad :p

I wanted to drive it in all conditions and for a couple days just to make sure that everything was actually ok, because that first startup thing was really weird.

---

Thank you to everyone that helped me in this thread, I really appreciate it. This repair is definitely the most challenging to diagnose issue I've had on this car, as well as the most difficult to fix due to sourcing the correct throttle.

The total cost of repair, after everything, was $640.

- Throttle: $440
- Rubber Parts/Hoses: $200

Which is much better than the scary original quote I got for $1,250 just for the throttle.

You guys rock, I have a few pictures of the install/parts, I was working alone mostly so it was hard to get. But if anyone in the future has a similar problem I'm happy to post them.

Thanks Again!
 

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#21 ·
Congrats on solving the initial issue. With respect to the weirdness (inability to start after it had been running) I think you are right; there is something going on in one or both of the distributors. Pull the rotors and and mounts and check the insulating disc that is behind them. The guys on the 500e board are very suspicious that these discs are failing due to age and the symptoms you describe are exactly what they talk about.
 
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#22 ·
Thanks for that info. By the discs you mean the reddish insulation pad located behind the distributors when you get the rotors/caps out?

If so, I actually removed those while initially diagnosing this issue and there was a bit of grime behind them. No scoring though. So I cleaned them up and put them back.

I've driven the car about 150 miles now since fixing it and it only did the not starting thing once right after replacing the ETA. Now it's starting if it's hot or not and it's clean. What I don't get is why the bulb indication light was on when the issue was happening? Very strange. If it happens again I'll order new insulators.
 
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