idle rough

[Cobra]

i took my intake off at work today to check out egr vavle seemed ok put it back together in a hurry (was on lunch) but i forgot to plug my IAT and MAF in remote started the van just before i head home got out there and it was idling fine but check engine light was on plug code reader in gave me a P0102 ok... easy enough turned it off plug them back in turned it back on idle was low again.... didn't think much of it drove home and parked before i turned it off i put my reader on it again and it said the intake charge temp was at 58F but the current outside temp is only 20F...? turned it off plugged the MAF and IAT out again and started it back up again seemed to idle normally....

So my question is can my IAT be causing my low idle i just pulled it ou and tested the resistence and it was at 4 that's at 20F seems wrong to me i now have it in the house and warm and it reads 3

edit 1: 8 pm the 9th and I just finished installing egr valve and test drive shows signs of improvment doesn't hesistate to shift up anymore at part throttle or at wide open (does that make sense...?). Idle is still really low when at stop lights and brakes are on put it in neutral and comes back up to where it should be, also seems the the idle is much smoother now used to miss alot when idlling low now only misses a little bit when voltage starts to drop to the red mark. (when i say idle low i mean around 650 rpm according to my jet programmer). Time to eat I have an IAC here maybe i'll put it in on sunday and go for another test drive.

[92astro]

update: i changed out my idle air control valve and it did not fix my low,rough idle problem when warmed up. it did fix my 3-4min high idle which was like 1500rpm for 3-4min. so i am thinking that it is my coolant temp. sensor for the computer or the o2 sensor.

[kings-x59]

been thinkin that since august, it's like 13 bucks, change it out.

[92astro]

you are talking about the coolant temp. sensor for the computer right??

[kings-x59]

yep for the 'puter

[92astro]

okay i changed my IAC and no change i narrowed it down to one of my modules the ignition control module which is under the cap or the ESC module i am gonna get the ignition control module tested first here in a couple of days then i will post back!!

[coolen]

Seems like you're having lots of fun. Before you loose your mind over this, for sure check your cts. My 94 astro that I have, once had a similar problem to yours, a bit different- but similar. I tried EVERYTHING I could think of. Changed plugs, wires, cap, button, throttle body, FP reg, injectors etc etc.... some of you here probably remember the post.

Anyways, what my problem was- was the actual connector for the cts. I went through many many sensors thinking that they were my cause, and I kept swappin' them out thinking I got "bumed" ones. However, like I said, it was the plug itself. After that, she ran like a charm, and still does. Well, not really, I changed the tires on it, ran it out of fuel, put fuel back in and no go. Not sure why, i don't think that it liked the rims and tires off my safari. And it hasn't started since...

Good luck

[92astro]

update: i changed my ignition module that is under the cap it did not fix my rough/ low idle when warmed up. i had the module tested it failed the bypass mode so i got a new. my next steps are to check the timeing and change my coolant temp. sensor for the computer and change my fuel filter since i have not changed it since 148,000 mile and i now have 178,000 miles. and for some reason one of the screws holding the ignition module in was broke so i had to remove the stud so my module is only being held in with one screw i will get a new screw but would that cause any problems??

[kings-x59]

It might. if the ignition control module is not seated well in the silicone that goes on the bottom side of it, it may overheat and die a premature death.

[92astro]

okay thank-you i will take care of the screw thing asap it is prettey chilli here in oklahoma so it should not be to bad. so what do you think about the rough idle now?? i am going to check the timing when the weather gets a little warmer. but do you think that it still could be my coolant temp. sensor? because how does the engines computer know when to go into closed loop like what sensor? and if it is the coolant temp. sensor could it give the computer false reading when it is warmed up?

[kings-x59]

yep it absolutely could give a false reading. pcm thinks the engine is cold when it's warm and runs it rich.
If I recall correctly, I think you mentioned that you smelled gas.
if you change it out, don't use teflon tape to seal it if it is a single wire sensor. The threads have to make contact to ground it. Seems to me, mine came with a bit of sealant in the threads. If not, use a bit of plumbers putty in the top half of the threads to seal it.

[92astro]

you might be right but it is not running rich as in blow smoke out the exhasut or fouling my plugs but how would the computer know when to go into closed loop???

[kings-x59]

You are correct, the ecm goes into closed loop when the O2 reaches temp and the coolant temp sensor reaches a preset temp. That preset temp is lower than normal operating temperature, at least it is on my '89.
doesn't have to run rich enough to blow smoke to make it run like crud. And maybe I've got it backwards, and it's running lean at idle. If the coolant temp sensor reports the temp higher than it is, or lower than it is it will effect the AF ratio. if the CTS is reporting a low temp yet high enough to remain in closed loop, the AF ratio will richen.

[Cobra]

i went under my van today to change CTS, Thermostat and blower resister couldn't get the CTS done but once i put the new thermostat it confirmed that my CTS was indeed working correctly still rough idle. so my question is how the hell do i find a vaccum leak i pulled the T under the hood apart while testing the CTS and it ran worse i plugged it with my finger and it improved. oh yeah it was warm out today so the symtoms showed up almost immediatly afer starting runs much better when cold or really cold out

any luck fixing it so far 92astro?

[92astro]

no luck yet but i picked up a coolant temp. sensor today and i am gonna put it in , in a couple of days and i will let you know the results. at my autoparts suppler they said that two blazers came in and had the exact problem as me and it turned out to be the thermostat and coolant temp. sensor. but yeah a vacume leak usally shows up all the time unless it is a gasket but even then you will still have issues. to check for vacume leaks spray carb cleaner around all vacume lines and sources and gaskets. if the idle changes then you have a vacume leak. here is a quick history of what i have done to my van to try to fix my issue: plugs, wires, cap, rotor,pcv,iac, air and filter, ignition control module,cleaned egr valve which was not very dirty that gives me the clue that the engine runs lean so that points towards the coolant temp. sensor and my van has never overheated this is a 1992 chevy astro Vin:Z 4.3liter v6 with 179,xxx miles.