Has anyone out there had problems with their engine control computer chip? My Diamante starts easily, then the engine starts to decelerate till it stops completely. My mechanic has ruled out culprits like alternator, coil, fuel system and thinks the ECU is bad. The cost of replacement is very high...have any of you had to replace one, and what was the cost?

:huh: i have a similar problem. my car drops rpm when i stop at a stop sign. when i crank it it idles perfect then low then finally settles.

Hai,
Did he do the basic checks like spark, injector pulse, wiring etc. Hope he checked the power and ground circuits on the PCM/ECM.I would also get a second opinion. There are places on the internet where you can send your old one and they will fix it and send it back to you.

Try cleaning the idle stepper motor, or replacing it. A common fault on these vehicles.

i agree the ISC motor causes problems, But be aware that the source of the problem could be in the ECU.. Just had an ISC go erratic and then fail with one coil open, but this was caused by a faulty driver IC Replaced the ISC (at some significant cost) and it was still erratic. and then figured out what was really happening before the new ISC was damaged.

On this ECU the M5269L drivers are replaceable and cost a few dollars.

Hello I am new to this but have been a mech for over 35 years, one problem is the capacitors in the ecu they leak and short, have someone with electronic exp check them out and replace if needed.( I had the same problem in mine and replaced the cap and it runs like it did the day it was built).

I changed them too and there was corrosion on the board where they had been leaking...seems like they are worth swapping before they fail completely.
Definitely runs better, I guess that is a combination of the ISC and the filter caps in my case. One opinion I got was that as the caps start to fail the ECU power rail is noisy and that can upset the analog info from things like O2 and knock sensors etc more than the digital stuff. Sounded like a reasonable idea.
Replacing all the bits was a fraction of the cost of a remanufactured ECU.