Just curious if an IAT sensor can have an affect on cold starting (been trying to figure out why my cold starts are a bit rougher than warm starts). During the cold start (whether 80 or 20 outside) it fires up within 1/2 sec of turning the key but the rpm briefly goes from 1100rpm to 800 for less than 1 sec then comes back to 1200 (this happens just once and immediately after it fires up on cold start). After that it goes to 1200rpm and stays there until warm (no idling issues either). Warm starts are normal (revs briefly to 1300rpm then drops to warm idle of 800rpm). Thanks!

 

your "IAC" could be sticking. remove from TB and clean it and TB with TB cleaner. Don't push/pull printle on IAC

IAC could also just be bad but you need a scan tool to determine if it is sticking to read IAC counts. Otherwise take a shot & just replace it but clean TB passage first

 

Ok....I just did this but while it was still on the TB (I took a bunch of q-tips and soaked them in TB Cleaner, then squirted a quick shot inside the IAC passage. Then I went around gently with the q-tips until I stop seeing so much black stuff coming onto the q-tips (even saw a little grit/dirt on one of the q-tips, wonder if that was built-up carbon).

10 really dirty q-tips later (TB plates were fine as I did clean them up recently), I let it dry for 10 minutes then put it all back together. Started it up, and it was a bit rougher but didn't stall (as expected when you clean the TB). Again, only takes a second for the idle to stabilize and from there on out, it's pretty smooth with no surging. To early to tell if it helped cold starts, but overall driving did seem a bit more responsive especially at just-off idle acceleration. Warm starts are still perfect, will find out what happens when it cools completely down.

I know it would've been better if I removed the IAC valve but it seems I'd have to remove the TB in order to get to it (since I don't have a spare valve I figured I would leave it on in case I break it).

 

you really need to remove TB to clean the IAC & specifically the point inside where the printle rests.

you can pick up a new TB gasket for a few $ at most auto part stores.

Typically just spraying the TB and IAC with TB cleaner and letting it dry is all you need to do

you may have done enough with your process to get it to operate right, good luck

 

At first I thought I fixed it, but it seemed the same when I started the car today (one brief stumble to 800-900RPM on initial cold start, but goes back to 1200RPM and stays there until warm). As a test I shut the car off after running for 30 seconds, and it started normal.

I guess I'll never figure this one out (warm starts are always normal). Oh well, no SES light and runs great!

 

Quick update -- if I only leave it running for 15 seconds, then shut the car down and restart, I get that same brief stumble to 900RPM then goes to 1200RPM. Run for 30 seconds or longer and I shut it down, it starts fine.

 

Ive always had a peculiar cold start issue myself.... When I start cold, it fires up, idles for 20 seconds or so, stumbles...sometimes hard, then idles normally. I found if I start the car, then quickly blip the throttle a couple of times, it never stumbles. Warm and hot starts, always perfect. I have replaced EVERY sensor on the engine...

 

Wow...mine are not this bad so I guess I should stop complaining!

My cold starts have one very brief stumble right after it fires up (goes to 1300rpm then drops to 900rpm, only once right after firing up on a cold start, then immediately goes back to 1200rpm and stays there (cold idle)....when warm it's 800-900rpm idle).

Was only hoping it's not an early sign of trouble (though the engine still runs perfect other than that brief stumble on cold start).

 

Mine is also only 1 time... its weird... Like I said if I blip the throttle once or twice, it never does it....Frikken finicky LT-1's

 

Starting to think it's related to the AIR pump since I noticed recently the dash lights dimming when the "RPM drop" occurs (the same time as when the AIR pump turns on during the cold start).

Thinking the AIR is drawing excessive current when it turns on. What should I be checking? Could it be the relay? Or the motor itself? I already had the recall done back in 2002-2003 so it is the updated design/components.

 

Tried changing the relay, didn't help (or hurt).

I may try removing the AIR relay next. If I try removing the relay, will the SES light come on immediately? What else turns on only on a cold start?

Also yesterday I restarted my "warm" engine after washing the car. The startup was normal with no surge that I usually get with the "left overnight" cold start. I also heard the AIR pump turn on and no rpm surge and no dim of the lights. So this leaves me with another question......what is the "pop" noise after the fuel prime when I turn the key on a cold engine? That "pop" is not there on a warm engine (wondering if that's related in some way). Thanks again for trying to help me with this strange cold start!

 

the lights dimming should of been put in your original post, have you checked your belt? alternator? also this is a pretty slim chance but also check the rubber on the crank pulley. i was having almost the same problem and it turned out the balancer pulley was turning on the hub for a few seconds when i started the car

 

Well....I only noticed the lights dimming recently (which made me think it's more of an electrical issue than fuel-related).

Belt is in good shape with no squeaks (goodyear gatorback, changed about 3 years ago when I replaced the belt tensioner (Dayco unit)). Power steering and A/C work properly too.

Alternator was just tested fine (it always puts out 13-14 volts consistently while driving, only drops if idle and in gear, and with all the lights on at night).

Is yours an LT1? Regarding the balancer pulley what should I be looking for?

 

Ok....it happens today and I also noticed the volts slightly above the 1 o'clock line (the one after 13). Is that dangerous? Does that mean something is wrong with my alternator??

 

yeah mines an lt1 take the belt off and see if you can get the pulley to spin on the hub, like i said its unlikely but it can happen

 

so how long are you going to F with it before you do what is likely needed which means take out the IAC valve and clean it and the part it goes into...Q tips are not a through job...

It is also possible the IAC valve is bad and hanging up...you would need to clean it & TB to confirm...or just throw $ at it and replace IAC. If it were me, I would spend $3 on a new TB gasket and clean the IAC and move on

if you had a scan tool to read IAC counts that would suffice...you would want to see if they stay high instead of dropping to 30-35 once motor is warmed up

 

after initial start up your volt meter would read higher than "normal". FWIW your gauges are for "reference" and not necessarily accurate. use a DVM to read wtf the output is on the alternator

and on the damper to see if the rubber is bad and damper is slipping, just make a mark across damper between parts of the rubber and rev/drive the car...if those marks don't line up anymore than the damper needs replacing. this may not necessarily be or have anything to do with your idle problem. just a simple check to see if your damper is worn and needs replacing