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89 260e 103 hard warm start rough idle

13K views 31 replies 10 participants last post by  HEESPAUL 
#1 · (Edited)
Parts I've changed:
-idle control valve, tested and works fine
-ovp relay
-tested the coolant temp sensor, is within spec
-changed airflow sensor potentiometer with new one
-fuel filter
-spark plugs
-replaced o2 sensor
-replaced valve cover gasket due to small oil leak
-checked all vacuum hoses, fine.
-adjusted the eha clockwise about 1/4 turn and even swapped with another, yet no difference in warm start.
-checked fuel pressure and fuel leak down; all within spec even hours after car was off, so no sign of any leaking fuel or bad accumulator or check valves.

car is 6-cyl 89 260e.

Starts fine when car has been sitting overnight (cold engine), starts up on first try, idle is above 1,000 until it warms up and stays smooth around 700-800.



When starting warm, fires up and cuts right off.

Tested the coolant temp sensor (for the computer) and tested fine at every temp listed in alldata temp chart.

When grounding the green/red wire for the coolant temperature switch with a 10k ohm resistor (simulating a cold engine) car starts fine on first try, even if engine is hot. This tricks it to think the engine is cold. And it starts up on first try and idle is close to 1500rpm.

Tested cold start valve and harness.


Any suggestions?



BTW, the car drives fine and has full power throughout on highway as well, just stalls sometimes when coming to a stop if I don't give it gas it stumbles and hesitates and cuts out.


Also, the engine (when hot), starts fine when tricking the ECU to think its cold (with a 10k ohm resistor), even starts fine if I disconnect the cold start valve in this case.
 
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#2 · (Edited)
You can rule out the O2/lambda sensor and the fuel mixture adjustment in about 10 -15 minutes. Click on the links to see tests.

That cold start throws extra fuel, maybe when the extra fuel stops the ECU is getting some conflicting info. And there are several input and output signals flowing in the ECU including: power from OVP, Idle speed air valve, EHA, Deceleration Shut off, A/C Compressor "On" , Coolant Temperature , Air Flow Sensor , Altitude Correction , O2 Sensor , RPM, vehicle speed, Check engine, Coolant temp...
Fuel Pump Relay behind battery
EHA: Electro-Hydraulic Actuator - Trims amount of Injection Fuel, Also controls Maximum engine Speed to 6200 RPM +/- 50 RPM; Top of engine, rear of fuel distributor

See the wiring diagrams for a better list.

Wiring Diagram: Electronic Engine Controls 118 118-1
 
#4 · (Edited)
The fact that your idle is above 1000 shows something is wrong. You should never see a start, cold or warm that is above 800-900. 650rpm +-50 is the correct idle speed once the car is warm and happy.

Check your idle control valve is not gummed up. Clean it out with some carb cleaner.

Car is stalling when coming to a stop...Was your OVP replacement a new or used? Stalling when coming to a stop is a dead classic OVP symptom....
 
#7 ·
Right, but I've tested the OVP and replaced it, also the problem is it idles low sometimes but other times higher, when low it does have a chance of stalling when stopping.

could the OVP be working right sometimes and not others? I never get the ABS light on even in these situations
 
#10 ·
Never, ever buy a used OVP. You are asking for problems with that. First thing you need to do is replace it with a new one. KAE is fine.

The ABS light generally means the fuse is toast and/or the relay is dead. It is != a functioning OVP if the ABS light is off.

Start with buying a new one and go from there. Like I said, I've experienced personally every stalling issue in the book related to the OVP, on both my cars.
 
#18 ·
All I am saying is that stalling when coming to a stop is probably not related to your issues and is solely OVP. I've stated my recommendation so up to you.

--

when you replaced the airflow potentiometer, did you position correctly and use the voltage as your guide? It must be very specific for position.
 
#22 · (Edited)
Could simply be the fact the cold start injector is spraying so the extra fuel is helping.

I think you have something going on with the ECU or EZL. Not because of the poor starting, but because of the 1000-1500rpm in drive. The system is holding the throttle plate open for some unknown reason.

Have you unplugged the EHA + O2 sensor to have the system in complete open loop?
 
#24 ·
Try another second hand ECU. Or borrow one from a friends car.
 
#28 ·
Is there a master list of things to check for this problem? Dieter does this to,I'm not looking forward to trouble shoot this problem
lots of threads on the internet with these cars dieing once warmed up
number one problem recommended is OVP,number two on the list is CPS
 
#29 ·
lots of threads on the internet with these cars dieing once warmed up
number one problem recommended is OVP,number two on the list is CPS
I'll admit I've only worked on these things off and on for about 20 years, but I think I've only replaced one
CKP (CranKshaft Position sensor) and never a CPS (Cam Position Sensor).
I did however get stuck at a Jeep dealer for about a year where I prolly changed one or two CKPs a week:crybaby2:
Are you talking a few minutes warmed up, or as soon as you go closed loop?
If it's puking as soon as you go closed loop, I'd be looking at O2 sensor, EHA, hung CSV, blah, blah, blah




Fish
 
#30 ·
Issue resurfaced again

I was wrong on my previous post on how I fixed this issue on my 1993 190E 2.6. The car was drivable for about 10 minutes and dies after it warms up. After inspection, I found that the issue was simply lack of basic maintenance. The problem is an ageing rotor and distributor cover. When the rotor is ageing the contact distance between the rotor and the distributor cover increase, and the distance also increase more when the car is hot. This is what happens when a car drive for a few minutes and then dies when it is hot.
I replaced my rotor and distributor cover and the car runs better than ever now.
 
#32 ·
engine random operation

M-B'z can be very finicky. It sounds like a dozen things. The only way I have found to fix these sort of random never the same twice is to just strat eliminating what it isn't. Look at every wire connection for corrosion. Clean the fuses and copper clips where fuses go. Check distyributor, rotor, wires. I have had them look OK but open hood at night and see if any spark is jumping. Check the micro switch at throttle linkage. It is an on off switch but plays a role. I think you could replace everyhing and maby not find problem. If you don't know what it is, determine what is isn't. Guessing get expensive and after 20 years of doing sdame I found it is something right in front of you and to sinpe to be considered. Good Luck, PW
 
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