Hard Start/Rough Idle

[MSimpson]

98' Lumina 3.1 liter V6 190,000+ Runs pretty good most of the time, but here lately when I stop at a stop sign or stop light it idles really rough and feels like my engine could die at any moment. Ever since I bought the car it's started really rough which I contributed to bad fuel injectors. ** JUST GUESSING** While experiencing this rough idle, if I throw the car into park the idle becomes normal.

Any suggestions?

I tuned up the car about 20,000 miles ago, and changed the fuel filter about 5,000 miles ago.

Thanks!

[maxwedge]

Runs rough is too vague to help on the net, but check for vacuum leaks, if you have a misfire like a plug or wire check that out, make sure the egr is not carboned up and holding off its seat. These are just some possibilities and yes an injector could be causing this, a full scan would look at misfire counts, may help pinpoint a cylinder.

[kevinb70]

-has battery been disconnected which will cause the pcm to have to relearn idle? (and didn't relearn idle correctly) I am inclined to say it's not that, because idle seems to be rough or stall in PARK, while in DRIVE the PCM seems to keep the idle smoother than in Park.

-how filthy/clogged is the throttle body including the passage way to the egr? to include the flexible tube leading from egr to the exhaust manifold. iac port could be carbonized and causing the pintle to stick.

-something with transmission causing engine to nearly stall when in Drive...

-note there is a vacuum leading down to the transmission (vacuum modulator) with a check valve... NOT saying it has anything to do with your problem, but check it for vacuum leak... and vacuum leaks elsewhere as well.

**I am still dealing with a idle relearn, which is why it first pops into mind. It's a bit better after I tried to 'retrain' it, but not completely OK yet. Mine stalls (or wont start) in park, but the PCM will keep engine running if I put it in drive. It starts/runs fine with very light pressure on accelerator. Been driving my truck during this week so that's not helping the idle on my car any! My idle problem didnt show up until about 10 stop/and/go trips, right at 50 miles after reassembly (and reconnection of the battery).

One request: just because I mentioned the IAC... DONT REPLACE IT. Alot of good parts are thrown away because of false diagnosis or just needed some cleaning.

[maxwedge]

The iac can cause a low or unstable idle, whether this is what you mean by a rough idle is unknown, I construe a rough idle as a misfire/shudder. Good points, kevinb70..

[kevinb70]

ya not exactly sure what rough idle means... he did mention it almost dying.

you can probably rule out the IAC by this simple test (how i get the car running when the IAC is acting up)

turn key on. press lightly on accelerator pedal. crank. if it cranks perfectly, then probably your iac or throttle body clogged up, especially if it acts like it is going to die when you let off the pedal.

[ladagosta]

Originally Posted by MSimpson

98' Lumina 3.1 liter V6 190,000+ Runs pretty good most of the time, but here lately when I stop at a stop sign or stop light it idles really rough and feels like my engine could die at any moment. Ever since I bought the car it's started really rough which I contributed to bad fuel injectors. ** JUST GUESSING** While experiencing this rough idle, if I throw the car into park the idle becomes normal.

Any suggestions?

I tuned up the car about 20,000 miles ago, and changed the fuel filter about 5,000 miles ago.

Thanks!

here is my 2 cents worth for what ever ..
I would also look at "check for vacuum leaks, if you have a misfire like a plug or wire check that out" as maxwedge suggested,,
plus look at relearning the ecu,, there is a thread on here on how to do this I will do a search and post it once i find it... it is recommended on seasonal tuneups..
after strattling a medium in NY in my Honda civic it tends to do this very thing.. not a rough idle but almost stalls out when i brake never does stall.. but almost nearly seems like it will but then finally regroups and continues to run.. cant figure out what has been disturb to cause this.. but oh well, she runs fine aside from a rattling noise stemming from the right side engine compartment or under the dash in the ventilating system and that almost stalling sensation..I can live with this minor annoyance

[ladagosta]

ok I can not find the post where it teaches you to relearn or reset your ECU.. but if I recall it is as simple as finding or locating the ECU fuse or fuses as some cars have more than one..

remove the fuse for seconds or minutees.. I would go with 15 minutes SOMEONE CORRECT ME IF I HAVE THE TIME wrong..

but more is better than less with this I am certain to be safe .. then replace the fuse and restart the vehicle and let it sit for 10 minutes runing then go drive around for a bit and that is all there is to it ..

it re-adjusts and reprograms to get better preformance .. supposedly.. I dont knwo for sure it hasnt hurt anything on mine when i did it ..

maybe it doesnt do a damn thing.. so let me know if anyone knows for certain..