Hi all,

Recently my car has developed a problem where it has a very rough idle but only when the engine warm! I've had issues in the past when it idled on cold, but after a good tb&isc clean plus new plugs, leads and a better cond dizzy it went away and runs great. However now, I've got issues on warm, Especially if turn the car on again when the engine has warmed up.

The idle on warm drops to 200-300rpm and feels like the engine is spluttering. Shakes are harshly into the cabin. Once you get moving there's some shuddering but I'm not sure its relevant to this issue. Otherwise she seems to drive fine.

Here's a brief relevant mechanical rundown of the car:
- All engine mounts have been replaced so that's not an issue.
- Spark plugs are IridiumIXs. Been used for 30,000km. Have checked them recently - no oil on them and has plenty of life left. Rhy look very healthy.
- Genuine leads recently refitted. Idle issue was before I ripped out the ngk plugs.
- Dizzy replaced with 2nd hand one as original one was caked in oil and have me cold idle problems.
- Tb & isc cleaned well less than 10,000kms ago
- Vac test done with gauge. Pressure was steady on 21kpa testing off the fuel reg line.
- EGR valves on rocker covers checked and recently cleaned. Solenoids were dismantled and cleaned. (maybe want out together right - I'll replace with so some second hand ones soon).

Could this all be the result of a vac leak or maybe a busted maf sensor?


Not sure if its relevant, but I do have a hissing noise on cold. It hisses on a cycle.

I'd really appreciate any help with this. I want the car to behave normally dammit!lol lol

Thanks!!

Maybe the hissing noise is a vacuum leak which from what I understand can and does cause rough idle

One potentially leaky place that makes quite a hiss if the O-ring is worn or damaged is the idle air screw on top of the TB. If you're missing the cap (fairly common) stick your finger over the cavity the screw is in and see if that changes anything. Cleaning the TB with carby/TB cleaner without first removing this screw can damage the O-ring, though I would have thought the ISC would be able to compensate to some extent unless the leak is really bad. Just something easy to check and eliminate.

Thanks guys for the responses!

Spetz - I'll check that with spraying some water or throttle body cleaner across the lines when the engine is running and see if the engine behaves any differently.

Ensoniq5 - Thanks for the help, but I'll need to have a look at my tb again to see which screw is on the top. I'll look around for any empty cavities.


Unfortunately this problem on idle got alot worse tonight.
On petrol, after about 15mins of driving, the car's idle gets very low and it struggles to accelerate off the line. It has almost no power for a few seconds and then the revs kick up to 2500rpm and then pulls hard like it normally would past that rpm. It feels like a very sticky throttle valve or loose cable. It's very difficult to drive the car this way, I need to keep dropping the clutch past 2000rpm.
I've got a similar throttle response issue on lpg, but the idle is fairly steady at 900rpm, however, you can put your foot down, and it's as if the car is starving for a second or two, and then responds to the input and acclerates.
I pop'd the bonnet up and pulled on the throttle cable, the engine seemed to have a delay between when I opened the throttle and it responding to the added air.

I'm tipping there's an issue between the crossover point where the air either passes through the main throttle body value or the isc valve. Might as simple as the ISC O-ring that's never been changed, or the unit might actually need a clean (would be surprised if it did because it was done less than 15,000kms) ago. I'm going to pull out the multimeter and test at which point does the TPS switch from throttle to idle. Might have to get a cheap 2nd hand ISC and TPS to test.
Anyone think I'm on the right train of though?

Idle air adjustment screw indicated by arrow below, however I only just realised you are running LPG about which I know bugger all!

http://s8.postimg.org/arlmxcpb9/image.jpg

No vac leaks or air intake leaks after the MAF? Ive seen it when a LPG car back fired and blew out one of the resonators on the intake. Popped it back in and re tightend and all was good.


Ive also had this starvation of fuel issue. But only on petrol. I had a bad batch of fuel, replaced everything and it improved but wasnt 100%. Replaced the oxy sensor too and that fixed it.