Running rough when cold


New Member
Dec 6, 2013
Raleigh, NC
Hey guys, need some help. My 92 LX runs horribly when its cold, but perfectly when its warm (this is an issue, because I need to be at work at 6a, and it is bad, but when I get home at 6p in the heat, its perfect). I have gone through the surging idle checklist, but the problem still exists. Here's its story:

My ECM failed last month - sent it off and had leaky caps replaced. Ran good for a couple of weeks after installing the rebuilt ECM. Then it started stalling right after starting it. I heard a bad rattle from the smog pump (bearings went bad), so I replaced it. Got some smog-related codes, so I went through the vacuum hoses and replaced a bunch of old and worn rubber. Cleaned IAC, set TPS, no dice. Replaced IAC, replaced ECT and ACT, checked timing (12 degrees), reset base timing, reset TPS (0.97), no dice. Checked 10-pin connectors, all looks good. It is stupid rich in the morning, and idles rich in the afternoon heat.

Alternator runs at 13.2V at idle, which sounds low to me. I ordered a stock crank pulley to replace the underdrive and will install it this weekend.

KOEO gave me my 11. KEOR kicked a 94 and 44. I intend to replace the diverter and check the thermactor tubes for clogs, but I'd like to get it running well first.

What am I missing?
  • Sponsors(?)


10 Year Member
Sep 1, 2010
Kearney, NE
At first consideration, the AIR codes should not make it run poorly when cold. It is adding air to the exhaust (post combustion) for emissions, specifically efficiency of the cats.
@jrichker any ideas better than going through the list again carefully and checking wires for continuity and low resistance from sensors to the computer?


StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
Dublin GA
" runs horribly when its cold" is very vague - does the engine backfire, have a miss, stumble or run just rough?

Have you set the ignition timing using a timing light?

Have you checked the fuel pressure?

Have you used a vacuum gauge to check the engine vacuum on a cold engine?

Have you run a cylinder balance test?


New Member
Dec 6, 2013
Raleigh, NC
Turns out that the ECM that I had rebuilt is bad. Swapped it with another that I bought for a spare, and it has never run better. Now, to chase down the warranty...