1994 Saturn SC2 Rough Idle when warm

DRIVERA1A

MEMBER
1994 SATURN SC2
4 CYL
FWD
AUTOMATIC
90,000 MILES

Idle's rough after warm while in gear. In neutral or park, idle is fine. No engine trouble codes are set. New IAC valve installed and run on road 35-50 for about 2 miles. Couldn't hold exactly at 40 mph very long due to traffic. How long does the auto reset adjustment take for new IAC valves?
Evap canister and hoses look good, no vaccum leaks there or with EGR. A puzzler. This is a used engine I replaced about 30K miles ago. Does engine require a reprogramming of sorts @ a Saturn dealership?

5 Replies

SATURNTECH9

MECHANIC
30,869 POSTS

If u replaced the engine about 30k ago and its been running ok then I doubt programing is a issue. So it runs rough at idle only it doesnt miss while going down the road?When it idles rough does it lose rpms or just feel like its missing like excessive vibration?When u replace the iac valve u just replace it start it and let the car idle it will run at like 3000 rpm then slowy idle down to normal. Let me know more so I can help u with ur problem.
Louie

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

Tuesday, October 13th, 2009 AT 7:00 PM

DRIVERA1A

MEMBER
4 POSTS

Thanks for the interest / help Louie,
yeah, the car runs pretty well and it is only rough when In Gear. If in neutral or park and idling after being warm, not a problem idles fine. Also Idles fine when first started and for the first 2-3 minutes. Maybe there is an ever so slight (very slight) hesitation on acceleration while driving. Yes when I replaced the IAC, and started the car, there was a short period of about 3000 rpms and it idled down as you described. Another observation is the exhaust seems a bit gassy. Relatively new plug wires, new plugs, replaced the coils. Any chance there is an issue with the transmission or a signal to/fro? I disconnected and cleaned off the electrical contacts visible from top behind battery with contact cleaner and reconnected. Regards, Ken

Was this

answer

helpful?

Yes

No

Tuesday, October 13th, 2009 AT 8:20 PM

SATURNTECH9

MECHANIC
30,869 POSTS

I was thinking u had a vibration issue since u only feel it when in drive if u have a collasped lower transmission mount. Also a collasped upper motor mount will cause a vibration at idle in or out of gear though. With it only in drive would be a collasped lower transmission mount my 99 sl2 vibrates only in drive at idle drives me nuts it needs a lower transmission mount.U have to be sure its a miss and not a vibration they can be tricky to tell apart unless u are experniced in telling them apart.U could check the coolant temp sensor its the second sensor down thats screwed into the head below the upper hose with two wires going to it. When the engine is cold u just squeze the connector and it should come right off look at the connector see if its green if it is u have to clean it some how or replace it. Sometimes the sensor cracks and leaks coolant into it causing it to short out and read lower then it should engine temp causing alot of differnt things overheat run too rich stuff like that.U could un screw it with the engine cold becareful u will loose coolant and lookat the the end that goes into the head and see if its cracked there less then 20 at the auto parts store if u buy on make sure u get one with a brass tip. Let me know what u find.
Louie

Was this

answer

helpful?

Yes

No

Tuesday, October 13th, 2009 AT 9:52 PM

DRIVERA1A

MEMBER
4 POSTS

Thanks again for reply Louie. Yeah, I have had a go around with the temp sensor and cooling fans. In the past 4 years I've gone through (2) temp sensor switches lower back (not the gage one-upper front). It got to the point where I actually ran wires to a light switch inside the car to control the cooling fan. (Jumpered fuse 6 or 7 a 30 amp to the proper fan relay pin). I ran like that for about a year and a half or so. After enough screwing around, I found that it was actually a looseness/positioning of the fuse relay center upper casing as it set on the lower casing. If I twist it just right, I can now cause the problem again. Anywho. I'll check the mounts as you've suggested.
Thanks again.

Was this

answer

helpful?

Yes

No

Thursday, October 15th, 2009 AT 9:37 AM

SATURNTECH9

MECHANIC
30,869 POSTS

Well theres always pick a part for that fuse box just find out which models and yrs fit and u can get one there cheap the fuse boxes dont go bad often.I get alot of stuff at pick apart its a fun place even my sister likes to go with me to get oarts for her saturn. When ever u replace the coolant temp sensor just make sure u get a brass one not the plastic one those bad alot quicker and if u have a choice of them buy the more expensive. Also on the mount I mention its on the bottom of the transmiission sitting on the sub frame. If u look at a new one at the auto parts store u will see the differance of how think the new one is. Well good luck let me know what u find.
Louie