LT1 idle issue
 

Ok, so here goes the one problem on my car thats been giving me headaches for about two years now. When I bought the car in 08, the car ran perfect, no problems, then out of nowhere, it developed an idle issue. When I start it, sometimes it will idle fine, other times it will idle real low, and when i go to pull out of the garage, it wants to die...then I stop the car, and the idle will come back up, other times, it will idle real high at first start up (2,000 rpms, or 1500) Other times ill be driving the car and ill throw the clutch in to come to a stop and it will idle at 2,000, then ill come to a complete stop, and sometimes it idles down, sometimes it doesnt. About 2-3 weeks ago, I took the car to the movies, after the movie, I hopped in the car to leave, started it....and it died instantly, started it again, but had to keep my foot into it to keep it running, but ran fine when i was going down the road with my foot into it. Ive replaced the IAC, TPS, IAT ( I replaced this, and it seems to idle low more often( around 500 rpm) but just the other day it was idling high), checked for vacuum leaks (I havent found any) my egr valve isnt stuck open, i can reach behind the intake and push it open, and it runs real rough then dies (as it should) I had this idle issue even with my stock TB, so i dont think its the 52mm, replaced the coolant temp sensor, I havent had any codes lately. A year ago tho the car threw an EGR code, wich I erased and havent seen it since. When the car idles high I can hear a hissing noise but its coming from the k&n filter...almost as if the enigne is trying to suck in to much air. Ive sprayed carb cleaner aroudn the intake, no changes in idle. And then there are those days where she runs absolutely beautiful.

Sorry for the long read.....any help?

I'd say small tear in the intake route or the idle control sensor needs to be cleaned on the tb but that is where i would start

Sounds like a bad map sensor to me. Check the sensor and the oring/gromet. Usually a good starting point.

I actually just did that yesterday, I pulled it off the intake, cleaned the the little o-ring gasket, and sprayed some MAF cleaner into a rag and cleaned around the hole, no change.

Then its the sensor itself. was it covered in oil?

Yea, it had some oil on it

swap it. the only thing that controls your tune is the IAT and Map. the O2s really dont do shit. stalling and shit. try for that first.

Speed density FTW!!!!

just replaced the map sensor.....still doesnt idle right, it started up and idled fine, but i took it down the road, and now shes idlin at 1500

I have an a4, and for what its worth, if i put my car in N and roll up to a stop it will idle around 1200-1500 until I come to a stop, then it will drop and idle around normal. Still trying to figure it out, seems like we have a couple similar problems but not all. If i figure it out ill let you know what to try.

Except my idle didnt drop when i came to a stop, it stayed at 1500

Whoops, I read that it would drop overly low and try to stall, didnt see that it stopped doing that and went the other way. My bad!

what brand TB is that? on my BBK the throttle linkage came loose and i had to re weld it. as after i hit WOT or let the peddle go too quickly the idle/throttle position would change. Should have picked up on that first. Sorry bro.

I have a bbk, but I havent had it come loose or anything like that. but when I took it for a ride after i changed the map today, i hit WOT many times, but the idle hadnt changed after that. The only reason i went to a bbk 52mm TB is because I tried to change the TPS in the stock one, but the bolts snapped off and then i napped a screw extractor off inside as well lol

but regardless, it still had the idle issue even with the stock TB

Ok, not to bring back the thread from the dead, but I THINK I FIXED IT!!!!!:sCh_elmodance: Last weekend I brought the car to 84ta406, and he checked all the sensors with a snap-on scan tool. All the sensors read fine, the IAC was a little off, so he adjusted it, the car was idling fine in his driveway. I drove the car through worcester on my way home, but the car was still running like shit almost 400rpm, then it was fine at around 850 rpm, then like shit again. So today, I tinkered with the trhottle position screw, I opened it up a little bit, took it out for a ride still a little weird, kept finicking with the screw, and took it out for a good half hour ride today, and she runs mint! Idk why that was the problem, cuz it idled weird with the stock TB....whatever. But now the car is running much better all together. before in between shifts, the rpms would dive, and the car would buck like crazy, now its smooth as butter. So now im just gonna friggin leave the car alone and drive the thing. WINNING!!!!!

Glad its running better, thanks to pizza about adjusting that.

Yeah definitley, I opened the butterflies a little more than we had em from your house and now its running ten times better.

problem is your intake IAC passages are now full of sludge. and you adjusting the throttle to "fix" it will for a while and in this weather. as soon as the da changes so will how it idles.

Essentially regardless of iac position. if the passages are plugged which can happen on an old 1993 intake. then the computer has no control over the idle. So id say take the intake off and check the iac passages. there are 4 threaded plugs on the bottom of the intake. take them out and run bailing wire or coat hanger threw them to clean them up. and then a good spraying of intake or brake cleaner. and that should do it.

what tipped me off was that with both the stock and the aftermarket tb's you are still having issues and now after moving the throttle blades(wich should have little effect on idle unless you go too far and over shoot the idle and TPS readings). it now idles ok. thats my guess.

Hmmm we'll see how it runs on another day, if it doesnt run right, then I suppose this is my next step.

First thing I thought when I read that, computer can't control the idle and your fix simply bypassed the issue.

Yeah, this all makes sense now. Thanks guys

just saw this thread I'd suggest first to take the tb right off and clean the shit outta it might be the IAC passages like pizza said my iac was junked up all behind the penis head it had a poopy shaft. Mine was gunked up to hell with oil sludge. douching the TB is def a good idea and its not a big job. it still didnt fix my cold start issue tho...

btw did you test your IAC

do you read before you post? ITS ALL NEW! :facepalm:

Haha thank you pizza, yea its all new IAC, IAT, TPS, MAP, and the TB is brand new as well, doesnt get anymore douched than that lol And I ordered Fel-Pro intake gaskets last night, just wating on those, and I'll pull the intake off. Any hints or suggestions to make the job go easier are appreciated, thanks again guys.

This led me to believe you guys were discussing sludge buildup in there.

Hes talking about the IAC passages in the intake manifold.

take your time. EASILY bend the head to head bypass tube up and out of the way dont take it off. you cant get the gromets from GM anymore. its the tube that runs down the passengers side of the intake and connects to the radiator near the filler cap. spray a light coat of pb blaster near the injector orings that seat into the intake. if they hevent been off in a while they will but stuck. try not to pry on them just twist and pull with your fingures and you should be good.

Thanks for the tips, I just got the gaskets in tonight, so I'll probably start sturday after school

U can get the gaskets free with a new cross over tube did it just before the motor let go in my car. Ha ha

ahh so they still make the tubes? Son Of A!!!!!

Yes sir

Alright, so I figured I'd update this thread. This past weekend, I did as pizza said, and pulled the intake off the car, wasnt nearly as bad of a job as I though it would be. The motor inside seemed very clean for 170,000 miles too. After I got the intake off, I took off the metal plate on the bottom of the intake, and took out the four plugs on the bottom of the intake. I ran a coat hanger through all the ports, and blasted the shit out of them with carb cleaner. I cleaned up the bottom of the intake as much as I felt necessary, cleaned all the gasket surfaces, put in new Fel-Pro gaskets and silicone on the front and back edges of the block. So after the car was back together, I started it up the next morning and she runs like a champ. No more idle issue, and my oil leak is now gone, it was leaking oil from the back of the intake (typical). So the Slowmaro is functional now!:sCh_elmodance:

Oh and I snapped a few pics of the motor with the intake off cuz I felt like it, theyre kinda shitty tho sorry.

Awesome Congrats on a job well done!!!

good job man!

great to hear guys

Well now that Ive been driving my car as my dd for the past couple weeks, it seems I did not fully correct the issue, it runs alot better than before, but it still likes to drop to low rpms (500) sometimes lower, and I sometimes still have the starting issue where I crank it over, and it fires real quick....then dies, so I have to keep my foot on the gas a little to start it, and once it starts, it idles WAY low like 300rpms. I honestly have no clue as to what could be causing this. It still sounds like the IAC isnt functioning properly.
any further suggestions?

Without re-reading the whole thread, did you ever try a known good IAC motor? And did you check the wiring to it for damage?

I did check the wiring when i took off the intake mani a few months ago, its all fine. The IAC motor in the car now is new but I bought it from advanced, idk if Advanced's parts are all that good, but I also had to replace the IAC connector on the wiring harness because the clip broke off the original. Im damn sure I have all 4 wires right, i used butt connectors, I would think that they are getting a good enough connection through those? The car did have the same symptoms with the factory IAC and connector.

also, just so noone asks again, Ive replaced IAC, IAT, MAP, TPS, TB is brand new.