Shakes at start-up

[juliana]

this is for '99 TJ 4L

for the first 2-5 min after i turn her on she's going through some serious shakes - from almost stalling to raving. if i hit the gas, she doesn't respond much, but the shake time shortens a little. if i start driving during that time, it feels as if i constantly hit and release the gas pedal. after 2-5 min of the shakes everything is back to normal - and stays that way until i turn her off. if i restart her after a short while she goes through the same thing, even though the motor is still hot.


she just had her throttle body cleaned, plugs and wires replaced, and got new distributor and starter in the process (grrrrrrrrrr). the jeep dude that did the maintenance couldn't adjust the timing right (no tools for that), so she ended up in the shop just for that. she was running perfectly for the couple following weeks, the shakes started a little over a week ago and are disturbingly consistent. "check engine" light is not on.

i have "sea foam" in her gas for the last week, i was thinking maybe dirty fuel injectors have something to do with the shakes, but so far the additive made no difference.

[RiponredTJ]

Juliana, you should bump your thread on JF. You're much more likely to get some answers over there. I still think could be an air leak, and it wouldn't hurt to rule that out.

[juliana]

just did. thank you, Alex.

[juliana]

just want to post this for future reference... it was a bad O2 sensor.

[Cutlass327]

Interesting that the bad O2 sensor would give you cold engine issues (open loop) - the ECU ignores it until it is up to temps and running in closed loop.