IveGotaCosworth

Hi all

I have recently refitted the head to my MY92 sierra cosworth and now when the car starts it instantly wants to idle at 3000rpm. to give you a run down of the spec is as follows:

Ported Head
Standard 4x4 cams
New belt fitted
Swedish plenum
New 3bar map sensor
Throttle body rotated 90 degrees (anti clockwise)
Uprated fuel pressure reg.

All my vac's are fitted to the plenum and as far as i know there is no air leaks. At first i had my ISV unpulled but now ive connect the plug the rpm still doesnt change.

I have backed the throttle cable right off to make sure the throttle flap is fully closed.

Before i took the head off the car ticked over correctly (even with a head gasket failure) and the only difference from then to now is the swedish plenum and the reroute of the IM wiring loom.

Im I missing something here which is staring me in the face....Pls Help.

Thanks
Andrew

cossiestu

I had that, I changed to a spare throttle position sensor and also cut out the 3 big plugs in the main loom, on the bulkhead... Not done it since, but don't know which bit cured it!?

Will Pedley Racing

If the idle speed is still 3000rpm with the idle valve unplugged then there is physically more air getting into the engine than there should be. To me that rules out an electrical issue (loom or sensor) at this stage.

With the fitment of the swedish plenum, has the throttle cable tension changed? If you're happy there are no air leaks then that would be the first place i'd be looking.

As a side note, you will need to have the fuelling checked as the swedish plenum will move a lot more air at higher engine speeds, that will cause a lean mixture.

IveGotaCosworth

Thanks for the info guys, i will check the voltage on the throttle sensor and totally disconnect the throttle cable to see if there is any difference and report back.

Thanks Again

IveGotaCosworth

Think ive found the problem......

Because the swedish plenum bolt holes didnt line up to the bottom section of the original IM I decided to have the two sections of IM welded together. What i havent realised upto now is that some of the holes did line up and i havent blocked those holes off... thus allowing air to be drawn into the manifold.

Will block the holes and report the results.

Thanks

johnnycortina

Just curious - would air being sucked in at manifold also show up as a boost problem as well - in that full boost pressure would not be obtained??

botters

iTrader: (2)

an air leak could cause that yes

Glenn_

iTrader: (1)

Have you cured the fault matey.

IveGotaCosworth

Hi,
Yeah if you had an air leak then full boost wouldn't be able to be obtained.

I haven't tried mine again yet as I needed to get the correct size bolts to plug the holes. I'm gonna have ago at it tomorrow n ill report back.

Cheers

martysmartie

iTrader: (1)

That isn't strictly true, whilst it can result in a boost leak it isn't impossible for the target boost pressure to be reached, that is the trouble, as the turbo is working harder to achieve the same boost.

OP your problem is an air leak, this is the ONlY thing to raise idle speed, as you have already eliminated the bypass valve.

Martin

IveGotaCosworth

Hi

Good news, once I'd capped all the bolt holes on the IM the over revving clear and the car settled to 1100rpm with an AFR of 15 with 3bar fuel pressure with vac off. The engine bled up quite easily too, the only thing to frustrate me was a noisy tappet. Hopefully that will clear.
Once I get het off the axle stands then wash n polish her I'm going to put the pics up that I'm taken along the way as a mini resto.

Again thanks for the help off everyone along the way