Car rough on idle, yet drives fine?

[TommO]

Hey,

My car idles badly..

It never stalls, but is very rough and feels like it's missing on idle. The idle speed often sits anywhere between 600 and 800rpm... it seems to be worse when cold, but is very unpredictable (sometimes it idles great, othertimes it doesnt).

Mods:

cat back exhaust

500hp walbro fuel pump

Any idea what could cause this? As soon as I start driving, the car drives great... just idles crap sometimes, and it shits me. (as I do a lot of driving in traffic / peak hour)

I was thinking injectors might need cleaning? The reason i'm asking on here is to try and save some money, don't have tons of it sitting around at the moment

Cheers,

Tommo.

[Zahos]

Before spending any cash, I would look into the following things

- cleaning AAC (cold start) valve

- check earth wiring on fuel pump.

- check Throttle Position Sensor (TPS)

All of these topics are covered already on the forum, so some searching will help you get some more detail. The first is very common on all EFI cars as they get on with age, and the second is common on skylines/nissans at the least, as I know they reduce the current to the fuel pump on idle, which can cause these problems if your wiring has coroded.

good luck

[TommO]

I actually just got new wiring put in (last week to go with the new fuel pump - a relay kit to run a solid 12v, and you can hear the fuel pump whining away

Thanks for the info - i'll have a more detailed search...

Cheers,

Tommo.

[timmeblackr32]

i had a similiar problem with my r32 and it was because there was a problem with my air flow meter. try and give it a clean (or get someone to do it for you), otherwise you may need a new air flow meter. i had to replace mine now it runs sweet as.

[predator]

I think most of them do that a little bit.. mine does.

I changed the AFM recently (not much difference), cleaned out AAC valve a few weeks ago. It runs perfectly smooth some times, few misses at others, but nothing consistent. Its nothing terrible, and I think it will have to be the compromise. If you are running a gap at 0.8mm maybe that is not good for idle - but you need it for running boost at higher revs. I'd rather have it idling a tiny bit rough occasionally, than missing under boost.

[Stoney85]

little to you knowledge someone put a set of Step 3 HKS cams in your car, wishful thinking

check the above mentioned things would be a good start

[turbohectics]

Check the hoses which go on to the inlet for the turbo where the blow off valve vents back to the front of the turbow mine was letting air in as there were no clamps on the hoses and also make sure afm is plugged in right don't laugh i left mine off once idled crap but could still drive and boost but had no go off boost ,

good luck champ

[TommO]

Yeah, i've tried:

- Cleaned the AFM

- Cleaning the AAC

- Cleaned the throttle body

- Then reset the ECU

Now it idles higher (800rpm or so, compared to 600rpm - I think I just need to adjust the idle), but is still a little rough.

I'll eventually get around to taking it to a mechanic and get them to check the TPS, O2 sensor etc, but for the moment i'll just put up with it

[gts4diehard]

My r32 does the same occasionally and also then runs perfectly when driving, there are so many sensors on this engine, that after 15 years could be running less than a 100 % - it could be a number of individual causes or a combination.

My frineds r32 has always done it, and now he has after market ocmputer, hi-flow turbo & exhaust, fuel pump, boost controller, dyno tune and it still does it. But I dont think he has changed his water temp sensors or any of the others.

My car idles perfectly most of the time then some times like crap, all it takes is a quick dab on accelerator then it will rise to about 1500 rpm then drop down to a nice smooth idle.

basically if everything else is going ok then dont worry about it.

I think most people just expect these cars to run perfectly after 15 years, which is unrealistic, especially considering the temps that all the sensors are exposed to under the r 32 bonnet, i.e. my car runs a perfect temp - always mid of gauge no matter what, but on a hot day and an hours driving you cannot even hold the bonnet support rod!

I can remember when I had a non fuel injected car(1970's Capri) that I was just glad it started on a cold morning, it was a pig until it warmed up, and when it was a really hot day and car was hot you would get hot- start probs due to fuel vaporising in carb/manifold! Cars have come a long way in that time but Heat affects all of us - mechanical and biological...

my own personal suspicion is that the engine temp sensor is not giving the right temp reading when engine starts, so it runs rough, but it could be all the other things people mentioned as well.

if you fix it let us know... as there are a lot of suspects in the engine bay.