Help! Bouncy idle (NEW PROBLEM READ NEW POST)

[Guest]

Edit : OK, I have redone the intake manifold using gasket goo.

My problem now:

When the cold idle valve is connected, the car has a 'wavy' up-and-down idle.

When the cold idle valve is disconnected the idle is steady. If I undo the screws and move it, it will raise or lower the idle. if I twist it completely anticlockwise, the car will stall or nearly stall.

What's wrong, why does it pulse from 2500-1500rpm when the cold idle valve is plugged in, but won't do it when it's not?

[Stoffa]

Sounds like a vacuum leak to me, you've got the purge valve/canister plumbed in right.

My guess would be dodgy inlet or throttle body gaskets if you've had them off.

Wouldn't hurt to give the ICV a good clean while your at it.

[Guest]

Took ICV off, used some gasket goo around both sides of the gasket, double checked the valve was installed correctly (it was according to FSM), refitted, no change.

Removing the TPS plug causes it to idle high (about 3k rpm) but steady???

Tried spraying CRC around various vacuum hoses, also tried removing some and blocking off or blowing through, can't seem to find any hose leaks. No change in idle even with vacuum hoses disconnected so the diagnosis of vacuum leak sounds about right to me as well.

A mate also suggested that doing the split fuel rail may have slightly changed the fuelling and as a result it's running rich/lean at idle and trying to compensate?

Unless anyone else has ideas of what to try I think I might just take it to a mechanic!

Edit: is there anything I can spray around various hoses that will diagnose a vacuum leak (by raising idle)??? Tried CRC but got nothing

[Guest boostin]

Split rail won't make it rich or lean, unless you've mucked something up. Have you sprayed stuff around the intake manifold gaskets? Might pay to pull the rails back off and check you haven't nicked an injector o-ring too.

Try using brake cleaner rather than CRC.

[Ryan]

I had the same problem and turned out to be intake gaskets. Have you fixed it?

[Guest]

Not yet. Suspects are either intake mani gaskets or a split in the intake pipe. Haven't had time to pull the thing apart again to replace either!

[Guest]

pete.. its a high possiblity its your power FC tune..

changing your fuel rail setup will have affected how much fuel is getting in to the cylinder as fuel pressure may have changed, so will have even put most of your fuel map out by a little bit.

Dom with the S15 had the same issue when cold.

Shouldn't take long to sort with a wideband and the powerfc software on the laptop

Give us a call and Aaron will be able to sort you out.

[log1call]

That theory sounds doubtful to me.

Fuel pressure is regulated. Mixture is controlled by the ecu not the fuel pressure.

If there are no trouble codes I'd suspect an air leak, faulty ISC valve(thermo spring perhaps), or a misadjusted butterfly screw.

[Guest boostin]

But the ecu is expecting 35ish psi of fuel pressure. If its getting 45psi it won't know until it hits closed loop and will run rich until then.

[log1call]

Yeah but just running rich will make it chuff and carry on but not really surge. Rhythmic surge will be ICV or air leak surely.

[Guest boostin]

Unless there's something wrong with 1 injector or bank??

[JWDRPN]

My car does the exact same thing with power fc been over a year still trying to find out why...one mechanic will blame the tune the other blames somthing else...it really bugs me id love to find out

[log1call]

So can you log these things as they are running? Should be easy to see.

One injector or even one bank shouldn/t cause a surge should it? The injectors fire too fast to cause a surge that you can time in seconds.

[Guest]

you can't do much with power FCs such as test each injector, put extra fuel in individual cylinders etc.. considering they were developed in like 96..

If you had FC datalogit then you can see the whole map and see what cells its jumping across

by changing the fuel rail setup fuel pressure may have increased or decreased. as fuel pressure increases more fuel gets in while the injectors are open so you car will run richer. but as fuel pressure increases injector dead time increases also.

A/F ratios and the timing around the idle cells cause this issue. If he brings it out then we may have an answer.

But yeah just bring it out pete, we can sit it in the dyno room, Put the wideband in there and plug the laptop in to it and then you might be able to rule that out as a factor and aaron can have a quick squz at the tune thats in there, although it could be good to chuck it on for a touch up tune if you have finished doing all your mods for now

[Guest]

OK, I have redone the intake manifold using gasket goo.

My problem now:

When the cold idle valve is connected, the car has a 'wavy' up-and-down idle.

When the cold idle valve is disconnected the idle is steady. If I undo the screws and move it, it will raise or lower the idle. if I twist it completely anticlockwise, the car will stall or nearly stall.

What's wrong, why does it pulse from 2500-1500rpm when the cold idle valve is plugged in, but won't do it when it's not?

[Guest]

lankilla had this issue when he put his possum link in, he sorted it by doing something. . . hope he shows up in here, coz i cant remember wht he did.

-smurff

[Munkvy]

Try another cold idle valve. As that sounds similar to the issue I had with a dead one in my car. We probably have a few spares at Steves place if you want to drop by at some stage and compare?

[Guest]

Might well do.

Update - if I disconnect the TPS the car will just sit at 2500rpm straight.

Measured TPS signal voltage and it's getting 4.7 or close to it with ignition on but car not running.

[Guest boostin]

TPS should be ~0.46V throttle closed, engine off.

Assuming V4 like your sig....

[Guest]

0.46? Oh, that might be my problem. I have an analogue multimeter though so I may be measuring the power feed instead of the signal....

[Guest boostin]

The feed should be 5V or just over.

[Pappu1]

 GETLOW said:

but as fuel pressure increases injector dead time increases also.

i never quite understood the theory on this one...? anyone can explain how this happens?

[Guest boostin]

For a higher given pressure, the injectors need to be open for a shorter duration to inject the same amount of fuel.

Injector open shorter = closed longer = increased dead time.

[nickmcgill]

I had a similar problem with mine,

Was told to do a upper cylinder cleaner, Not much difference.

Cleaned the ICV out with upper cleaner in the chamber and brake cleaner on the " bullet " and arm etc.

Still no change.

Then was told about how the TPS should be set at ~0.45v for mine, Did that and its cleared it up 90%

Think its just spark plugs now lol.