Cold start rough idle

Hello.

1st time post.

I am stumped on this one…..99 Toyota Camry, 4cyl., LE + 240,000 mi.

Hard or no start when it turned cold. I replace PVC and PVC grommet. Now just a rough idle.

After I replaced the PVC & grommet, the car starts OK. When its warm outside and the engine is cold, the car starts and runs fine.

HOWEVER…..when starting cold, if it gets the least bit cold outside ……20 degree F or less) the idle goes rough and if I give it gas it stalls. After it warms up at idle, all is OK.

On warm days no problems at all.

This all leads to something related to temp…. right.

I just went out to car and started it (approx 25 degrees outside where car is now) and car started fine but again a rough idle after the cold start.

I then unplugged the IAC and the idle sped up and smoothed out…..plugged it back in and it went back to rough.

Note, one week ago, I replaced the IAC with a brand new after market IAC and replaces the ECT sensor also aftermarket.

What does the car running smoother with the IAC unplugged indicate?? Bad IAC?? Bad ECT sensor (also just replaced with after market …Advances Auto).. Any ideas??

Any suggestions will be really be appreciated.

Here is what I have done so far:

Checked for vacuum leaks after replacing PVC grommet…no leaks at all.

Note I did not get behind engine to check the VSV for the EGR since that is not temp related.
Also, car idles and runs perfectly when engine has warmed up.

Replace spark plugs, checked wires and coil packs…all OK
Replaced IAC (aftermarket)
Replaced ECT sensor (after market)
Replaced fuel filter
Checked throttle position sensor…OK
Checked and re-set to manual all Throttle body settings (idle + throttle opener setting speed) all OK
Checked fuel pressure…OK
Checked IAC connector power from computer….OK
Checked temp readings with scanner…OK
No trouble codes thrown

Finally, before installing I checked both the new aftermarket ECT sensor and the new aftermarket IAC per the Toyota manual. Both checked perfect.

I watched fuel trim at cold idle and here is what they were:

Short: -1.6 to +2.3
Long 6.2

My scanner says this about O2 sensors , measured after engine is warm (close loop):

Low volt switch time = 0.400v
High volt switch time=0.550
Min sensor volt= 1.275v
Max sensor volt=0.000

I do not know what the fuel trim and or the O2 sensor numbers mean or indicate.

Note, I ruled out O2 sensor as a cause for rough idle, since the car idles and runs fine when warm and in closed loop

Cannot figure what’s causing the “cold” rough idle. Confused in Ohio! :huh: Any ideas??

Thanks,
Joe