Idle and hot ignition

[bluejay]

When idle is down to normal (900revs) there is a popping sound out of the exhaust. I've ben told it's unburnt fuel entering and it's pretty normal????

I don't know if it's connected or not, but when the engine is hot and switched off for five minutes, on restart, it starts straight away, but struggles to find it's idle lvel and usually cuts out.

[mike_sekinger]

It sounds more likely like you are having a small misfire. When the car is idling, there should not be unburnt fuel... unless you have some fuel leaking into the plenum from the the secondary injectors.

What is the state of your spark plugs - are they sooty and showing any rich running?

Cheers,

Mike S

Edited February 8, 2012 by mike_sekinger

[bluejay]

Thanks for the swift response Mike,

Plugs are new. Been in Lotus dealer but everything seems fine. The car always starts and runs well. It's just annoying at idle with that pop. Even when hot it starts straight away but struggles to maintain revs without throttle.

Thanks,

James.

[V8 FOU]

If there is an air leak in the exhaust system you will get a pop.

The injectors maybe leaking while closed - a common problem. Try a good fuel system cleaner and only use best quality fuel.

An injector clean / test may help. (I have a cleaner tester/cleaner in my w/shop....)

A afr test will show if you are getting unburnt fuel in the exhaust on idle with a high HC reading, conversely a high O2 reading if there is an air leak. Any MoT type tester will show either of these.

High HC will destroy your cats btw - so it would be a good idea to investigate asap!

[bluejay]

I hear what you are saying Paul. I have new sports cats and straight pipes out fitted. The problem was there before these. I only use the best(and most costly) fuel.

With the hot starting issue, I'm wondering if the o2 sensors are dodgy, and telling the engine it's too rich and the management leaning it out too much. When it was in at Lotus they said it may be running a little rich, but nothing to worry about. I presume they would have checked all you said.

Cheers,

James.

[ramjet]

I sort of suspect a sensor somewhere based on what you said about the hunting when hot.

[V8 FOU]

I hear what you are saying Paul. I have new sports cats and straight pipes out fitted. The problem was there before these. I only use the best(and most costly) fuel.

With the hot starting issue, I'm wondering if the o2 sensors are dodgy, and telling the engine it's too rich and the management leaning it out too much. When it was in at Lotus they said it may be running a little rich, but nothing to worry about. I presume they would have checked all you said.

Cheers,

James.

I wouldn't presume too much I'm afraid. Do get the afr checked out before you do anything else. Any half-decent OBD tester will be able to read what is going on with the O2 sensors (disconnect the post sensors before doing that).

[bluejay]

Now here's a strange twist to the tale. I was stopped at roadworks for a while and the engine was popping away merrily. The fans came on and lo and behold the popping stopped. It started again a short while after the fans stopped. When they came on again, the popping stopped. Stumped, I am!

James.

[V8 FOU]

That's going to be IAC related. When the fans come on or the a/c switches on, the ecu increases the idle speed a bit, so I would look at the idle circuit - possibly an air leak.

Try spraying some intake cleaner around the area while idling and see if it smooths out or increases its speed.....

[bluejay]

Thanks Paul,

Where exactly would I be spraying?

James.

[bluejay]

Tried switching the air con on but it made no difference, still popping, only when fans are on does it stop.

James.

[V8 FOU]

Thanks Paul,

Where exactly would I be spraying?

James.

Sorry I didn't spot this earlier. If you are still having trouble, spray carb cleaner around the throttle body and the pipework for the iac.