Rough Idle

Finch204

Finch204

Greenie N00B Member
Greenie Member
My car is idling roughly, usually when I'm on a stoplight. This only happens when the engine is already warmed up. Doesn't seem to happen during cold starts or when the engine is below 180F coolant temp. Check engine light is not on and there are no trouble codes. My car battery was fully charged last month.

Looking at the Accessport when this happens:
  • I see my AFRs go a little lean. It will spike up to like 15.23 or 15.34 or 15.45 then drop back down to the 14s.
  • At times before the AFRs spike up, the LTFT will go up then back down to its normal idle value.
  • The battery voltage at times also drops down to like 13.4-13.6 when this happens. Yesterday it dropped all the way down to 13.0.
  • While all that is happening, the car is vibrating more than usual. It is not the same as when the AC compressor kicks on. It is a noticeable vibration or like I said, rough idle.
Might be unrelated, but I also have an issue of a somewhat hard start. Car is taking longer to start later in the day. Doesn't seem to happen in the morning, but it happens during my lunch break or before going home from work.

Does anyone have an idea of what's wrong here? Do I need a new alternator? Do I need to clean my intake valves? Bad oxygen sensors? (I still have the oem downpipe)
 
check your battery, mine was doing some similar things and i didn't figure out that it was the battery until i went on vacation for a week and came home to a dead car.
 
Easter Bunny said:
check your battery, mine was doing some similar things and i didn't figure out that it was the battery until i went on vacation for a week and came home to a dead car.
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I had my battery fully charged a few weeks ago, so I didn't think it was the battery. But I'm getting a battery tester soon, so I'll double check that.
 
Been awhile since I've updated this thread. The battery is fine. Had my throttle body and intake valves cleaned a few days ago. There is an improvement with the rough idle and the car's performance overall. However I still have the issue with the hard/long start. It only affects the car during the day, like on my lunch break or before I leave work for home. It doesn't affect it on cold starts. Since I have not been able to do an EGR clean yet, I was wondering if disconnecting the EGR plug would be an okay temporary solution? At least until I can either delete my EGR or have it cleaned.
 
How many miles on the motor? What plugs you running & when were they installed and gap are they at now? Do you have any issues when getting into boost or is it literally just hiccuping at idle once warm?

In addition to the EGR could also look at purge valve too as I know that's been known to cause idling trouble when it goes bad.
 
Josh Smith said:
How many miles on the motor? What plugs you running & when were they installed and gap are they at now? Do you have any issues when getting into boost or is it literally just hiccuping at idle once warm?

In addition to the EGR could also look at purge valve too as I know that's been known to cause idling trouble when it goes bad.
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I have 80k miles on the engine. I am running stock heat range plugs and gapped to oem specs. I was previously running one step colder plugs and still had the same problem. Plugs were changed at the same time that the throttle body and intake valves were cleaned. I do have issues when getting into boost. On my custom Dizzy Tune map, the throttle is so sensitive that usually the car hesitates when accelerating or getting into boost. I either have to be fully committed to hauling ass or not. If I sort of try to modulate the throttle, the car will hesitate because boost builds up too fast then drops. On my Stratified flash tune, this is less of an issue for some reason, but is still there.

It is interesting that you mentioned the purge valve. When I was researching the EGR valve issues again last week, I ran into someone mentioning a problem with their purge valve with very similar symptoms. I didn't think much of it, but I will look into it some more.
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JohnnyTightlips said:
Fuel pressure at idle?
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It is around 200-400 at idle.
 
Finch204 said:
I have 80k miles on the engine. I am running stock heat range plugs and gapped to oem specs. I was previously running one step colder plugs and still had the same problem. Plugs were changed at the same time that the throttle body and intake valves were cleaned. I do have issues when getting into boost. On my custom Dizzy Tune map, the throttle is so sensitive that usually the car hesitates when accelerating or getting into boost. I either have to be fully committed to hauling ass or not. If I sort of try to modulate the throttle, the car will hesitate because boost builds up too fast then drops. On my Stratified flash tune, this is less of an issue for some reason, but is still there.

It is interesting that you mentioned the purge valve. When I was researching the EGR valve issues again last week, I ran into someone mentioning a problem with their purge valve with very similar symptoms. I didn't think much of it, but I will look into it some more.
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It is around 200-400 at idle.
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Idle pressure should be close to or just over 400 pretty much all the time. Check spill valve and Relief valve. LINKY1 LINKY2 , if you do clean it use THIS to clean and THIS to lube. 200 is too low. I had my relief valve go out with similar issues. It is a common problem at higher miles. If you take it out and can blow through it then it is bad. CHEAPEST VALVE
 
If your HPFP is looking pretty cruddy I can vouch for a local guy to me, Wes. He disassembles, deep cleans, and replaces every gasket within which I don't think anyone else is out there offering this kinda service??. He has a pump swap program where he ships you a basically flawless pump that he's cleaned and you swap your internals in and send him yours, and he charges I want to say around $70-80?

Here's a link to his fb: https://www.facebook.com/wes3id/

I'll include a picture he shared of some of the pumps he's cleaned.

As for my car - my idle fuel pressure is about 400-420 psi. Under WOT since I replace my pump with Wes' w/ autotech internals sits around 1750-1800.
 

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JohnnyTightlips said:
Idle pressure should be close to or just over 400 pretty much all the time. Check spill valve and Relief valve. LINKY1 LINKY2 , if you do clean it use THIS to clean and THIS to lube. 200 is too low. I had my relief valve go out with similar issues. It is a common problem at higher miles. If you take it out and can blow through it then it is bad. CHEAPEST VALVE
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I said it was 200-400 because when I look at the minimum fuel pressure value on my AP, the minimum value was around 200. I was monitoring it today and it seemed to be above 400 while I was idling on a traffic light. I'll monitor it for a few more days. Thanks for the links!
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Josh Smith said:
If your HPFP is looking pretty cruddy I can vouch for a local guy to me, Wes. He disassembles, deep cleans, and replaces every gasket within which I don't think anyone else is out there offering this kinda service??. He has a pump swap program where he ships you a basically flawless pump that he's cleaned and you swap your internals in and send him yours, and he charges I want to say around $70-80?

Here's a link to his fb: https://www.facebook.com/wes3id/

I'll include a picture he shared of some of the pumps he's cleaned.

As for my car - my idle fuel pressure is about 400-420 psi. Under WOT since I replace my pump with Wes' w/ autotech internals sits around 1750-1800.
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I have not checked my hpfp. Is this something that will also need regular maintenance?
 
Finch204 said:
I said it was 200-400 because when I look at the minimum fuel pressure value on my AP, the minimum value was around 200. I was monitoring it today and it seemed to be above 400 while I was idling on a traffic light. I'll monitor it for a few more days. Thanks for the links!
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I have not checked my hpfp. Is this something that will also need regular maintenance?
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HPFP does not need regular maintenance. Mine is at 150k with no issues. It can get gummed up if you run a lot of ethanol like 40% or greater blends. It is still a place to start though and if it has never been cleaned you could do what was suggested. I did my hpfp internals at 135k and the pump was hardly dirty with just minor blemishes.
 
I do know a lot of folks recommend occasionally cleaning the spill valve with some fuel system cleaner and cotton swabs. I disassembled mine and cleaned mine by hand at 137k and mine looked super gunked and nasty and thats only ever having run 93 fuel. So I think it just depends. I'd definitely recommend at the least cleaning it out if you're seeing pressure drops under wot.
 
Memin said:
OP what was the final outcome on your issue???????????
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If you mean my issue with hard starts, it has gone away since it started getting cold here in Texas. It was really bad in the summer, but does not seem to be an issue at all the past few weeks. I will report back if it happens again. I didn't do any fix for it. I was supposed to drop it off at a dealership to let them take a crack at it, but like i said, it has stopped happening after the weather turned cooler.
 
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