Hi!

Just two weeks after replacing my DME for a new modern unit from ECU doctors (solving a ”no start issue”), my car suddently died at idle on my way to work.

It would just suddently die on idle and sometimes it would manage to recover.
Sometimes it will just start to idle about 1800 rpm, I’ve noticed a lot of smoke from the exhaust when it do so, and ever so slightly touching the throttle would instantly kill the motor.

If I stop shortly to refill gas, it might take some seconds to get her fired up. This is also the case some of the times when it just have randomly died at idle.

If i keep some gas and keep her about 1000rpm, the issue never comes.

At rare times it will also ”cough” when just starting to accelerate from about idle speed.

Since the first day, the issue have not noticable become worse or better, but it can vary a lot from day to day. I can sometimes go on a 15-30 min ride to work with no issue, sometimes it start having issues just minutes after starting the car.

Before replacing the DME, I already replaced:
DME relay
Fuel pump
Fuel filter
Earth cable to chassis from transmission
Spark plugs
Spark plug cables
Rotor
Ignition cap
Ignition coil

and cleaned the ground points, checked ohm readings om ground wires and injector cables.

Since this new issue arrived I have also tested to switch back to the old coil, fuel pump and DME relay.
If I bridge the relay to constantly run the pump will not take away the issue.

I have tested to measure the voltage on the battery and fuelpump simultaniously to check for suddent voltage drops when the car dies, but it keeps unchanged.

I have recently changed:
Fuel pressure regulator
Cylinder head temp sensor
Idle control valve

I have also replaced the Speed and Reference sensor with each other to see if I would have another issue, but they remain the same.

The idle goes down when I remove the oil cap so the vacuum should not be horrible, but I can not rule it out yet.

Since the fuel pump voltage does not drop, the oil pressure switch (that grounds the fuel pump) should also not be causing the issue.

I will buy a smoke tester to look for vacuum leaks.
I guess the fuel pressure dampener is also a contender. Is that available to buy somewhere in europe for an ok price?

Any other suggestions?

 

Sounds like you need to call them, about the " new modern" thing.

 

This is the DME I bought from them:
https://www.ecudoctors.com/products/...utright-sale-b

They have offered me to send it back, and I’ll only pay a inspection and return fee if the unit is not faulty.

Being without the DME is a bit annoying since the car is normaly my daily driver, I really want to rule out easy to check/fix problems before sending it away.

But thanks, I’ve printed the return form now.

 

What happened to the OEM DME ECM? They are very reliable and rarely need replacement, other than for water damage. A repair is typically less than $500.

 

No company answered when I emailed, except for one that would not touch it because it had been opened before.

No water damage.
I had no square wave signal to the injectors and it would not send a signal to the DME relay to run the fuel pump.

I believe it was the S400 0127 IC that was damaged, apparently a common issue after the transistors to left and right bank of the injectors.

 

Check here; https://rennlist.com/forums/911-foru...warm-help.html
There're numerous sources as noted on Pelican Parts! One that's been repairing for over 35 years.

 

I would definitely start with a smoke test to verify that you don't have any intake leaks.

when you replaced the ICV, did you go through the manual procedure with the installed jumper between pins B and C when setting the base idle?

 

That has very little effect on the engine continuously running, i.e. it only tweaks the idle RPM.

 

Did you check your air meter? After a lot of troubleshooting on similar stalling issue, it wound up being that. Link below to my thread.

https://rennlist.com/forums/911-foru...d-startup.html

 

unless you set too low and the ICV doesn't have the range to compensate. Any time someone has an idle issue, I feel this is worth mentioning. It is a simple procedure and will make sure the engine is in the correct configuration to troubleshoot from.

Sure, you may be able to get away with a random bypass screw adjustment when everything is working correctly, but once you have an issue and are going to try to troubleshoot, you need to know what point youre working from.

 

I did set down my idle and got rid of some hunting (pulsating), but I think I'm about right at the idle according to the gauge, but maybe better to measure with an external more accurate gauge?
I've ordered a smoke tester today.

 

Did you set your idle per the manual process with the jumper in place?

 

Correct!

I also tested my friends AFM yesterday with no change in result at all. (Same Bosch part nr)

 

Do this test for your idle problem;
Idle Valve Testing, post #20, http://forums.pelicanparts.com/porsc...rol-valve.html

 

the ICV is brand new, it did not make my issue go away, still identical.

both the new and old produce the humming vibration, but there is a slight, but noticable pause once per second when only the key is turned but before starting the engine. Is that normal?