This is really starting to drive me crazy, but I'm trying to eliminate a problem that I'm having with my ECM. I started out (about a month ago) with the traditional '93 ECM problem where the security light and sys light blinks on the dash while I'm driving. If that condition exists when I (attempt) to start the car the security system holds the car out from starting. This has happened before (3 years ago) it was time for an ECM replacement. There was (is) a national shortage on rebuilt '92-'93 ECM's so I did the research for a decent company to rebuild my unit, and I decided on SIA electronics. After sending my ECM in the first time, when I received it back, installed it, the Idle went up to 1500 RPM and would not come back down. I did the factory "IAC Reset" procedure to zero the IAC valve and that did nothing. I then sent the ECM back for rebuild again, and when it came back for the second time I had the exact same problem with the idle. I then checked the OHM reading from the plug to the IAC valve for the low and high circuit and both met factory specs, I also replaced the IAC valve and still no improvement. I had a spare EEPROM, swapped that out and no change. I manually moved the original IAC valve in to slow down the idle (so the car is driveable) and after driving the car for ~200 miles, now the SYS light is back again!!! So not only have I not made progress forward, but I've now made a step backwards...

I still believe it's the ECM, and now I'm faced with sending the ECM back for a third time....I talked with the rebuilder and each time he rebuilt the unit he found something else wrong.

What other options do I have at this point? Does anyone know where I could find a (reasonably priced) NOS ECM?

Is there anything that I missed?

Any thoughts would be appreciated!!

 

I think about a week or two ago there was a post similar in that one system was not talking to the other and that person I believe disconneted all modules and plugged them back in one at a time to see if he could pull codes or the data bus was flakey. If one unit shorts the data bus or pulls it high I would think nothing talks though could be wrong on the nothing.. I the ecm and ccm don't talk could the fault of either one. You might try a search on ccm or ecm or data bus to find it and see if any clues are there..My 91 had a score of codes when I got ti last November and a cheap scan tool and a set of shorting plugs from Corvette central though sure others sell them was a lifesaver for me. Like with your idle problem the scantool will tell you what is being commanded to the IAC. The book that comes with the plgs has all the fault codes in one thin book and easy to read and i believe hints as to what is normal and what is not.. It might not be the ecm.. Think I did see one on ebay the other day as looking for a complete spare for the 91 and thought there were som 92-93 pieces forsale. Might be worth a look..Or a salvage yard and get one complete with memcal and see if it runs..

 

Davies corvette parts & accessories,had rebuilt ECM's 2 weeks ago,I bought one for my 93