Supercharger and fast idle

DBM58 · Post by **DBM58** » Fri May 26, 2006 12:05 pm

Late last year Matt Avery and I swapped cars meaning that I now drive a vivid yellow car loaded with all manner of MazdaSpeed extras, including a supercharger. As far as I can understand, the car has always had a problem with a fast idle, around 1500rpm, that a number of learned people have had a look at, but with no success. It is also hard to keep the engine running when it is cold. A suggestion that Matt made was to fit a three-wire oxygen sensor to solve the cold start problem.

Can anyone offer any more advice, particularly with regard to the fast idle.

Thanks

DBM58 · Post by **DBM58** » Fri May 26, 2006 12:11 pm

By the way, I do not mean to infer that Matt gave me a car with a problem, I was fully aware of it at the time. It has now come time to fix it.

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Post by **jif** » Fri May 26, 2006 2:19 pm

Hi Dave

what has been ruled out already ?

I imagine that they've already looked at idle screw and temp sensor? What about vacuum leaks? Is it there to address the idle dip problem that some SC have ?

Jeff

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DBM58 · Post by **DBM58** » Fri May 26, 2006 3:35 pm

Glenn identified a problem with the idle screw, and complete lack of adjustment. This has been fixed. Can you explain more about vaccuum leaks.

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Post by **jif** » Fri May 26, 2006 4:18 pm

if you have an vacuum leak it sucks in air through a cracked/loose hose, for example, giving the same result as opening up the idle screw. Possibly worse if the sucky air is after the airflow meter, meaning the ECU doesn't know about it, causing the mixture to be off.

The trick to identify this is wave cig lighter gas around the intake plumbing and see if the idle changes as it's ingested. (so I hear)

OT: I have a Mazdaspeed badge for cheap if you fancy it - let me know :]

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SLYDIT · Post by **SLYDIT** » Sat May 27, 2006 10:26 am

ive been thinking about this and definitly sounds like a vaccum leak. basically all points after your air flow meter need to be totally leak free or youll have problems.
first id look at the rocker cover breather that goes from the rocker cover to the inlet manifold and also the hose on the other side that SHould go to somewhere after the afm but before the S/C.
remove the inlet manifold to rocker cover hose and block it with your finger while an assistant starts car to see if its sucking air in from the PCV valve.

Possible leak areas.
PCV system as above
Injector o rings
Rubber nipple cover on the rear of inlet manifold, that points towards the fire wall,(its hard to see but is down by the clutch master cylinder on the #4 cylinder runner) that often blows off in S/C and T/C cars.
JRSC throttle body dummy on inlet manifold.
Charcoal canister vac line( just behind RHS headlight)
any lines connected to the two little ports by where the throttle body was.
Small vac lines that control the S/C bypass valve.
the large silicon couplers on the afm and charge pipes.
May sound silly but if your system is all sealed up but the rocker cover gasket is leaking. it can actually suck air in past the rocker cover gasket.Have you had a polished cover fitted?

Are you able to post a pic of the engine bay??
Id also get a heated Oxygen sensor..it made a world of difference on my car.

DBM58 · Post by **DBM58** » Sat Jun 03, 2006 9:53 am

Thanks for taking the time to reply.

With regard to the two hoses from the rocker cover, how would you tell if there was a tiny hole, or is it easier to just replace them?

And the heated oxygen sensor, where did you buy yours from, and where did you take the power wire from?

Thanks

Regards

David

SLYDIT · Post by **SLYDIT** » Sat Jun 03, 2006 1:53 pm

with regard to hoses etc, just get the running and pull them off and plug both hose end and nipple with your fingers, if the idle improves then thats where your problem is.
I got my heated oxygen sensor from a wrecked car at pick a part for $10.

new they are $150 plus...
they are easy to spot as they have 3 wires coming out of them(usually two white,one black or vice versa) instead of the usual one. most cars post '96 and also earlier euro cars have them. but make sure its a BOSCH one as the heater element is 12 volts. some of the nissan heated ones are only (8 volts?)have red/white/yellow wires and dont work.
i just hooked the oxy heater feed to a switched 12 volt wire feeding the ecu.

poison · Post by **poison** » Sat Jul 22, 2006 7:18 pm

While out and about today in the MX I bumped into an electronics controls wiz I deal with through work. He saw my car and started asking lots of interesting questions sbout my Turbo set-up and seemed to know a lot about ECU's and car performance in general.

Turned out he worked for Bosch in Europe as a designer/repairer and that Bosch make a lot of ECU's and the software for a lot of manufacturers including many in Japan and much like standard parts many are rebadged to Mazda or whatever.

Anyway just about the first thing he said to me was 'oh you need a new oxygen sensor' I asked why and he said 'because it's over 5 years old and the performance drops off markedly about then'. Wow I knew sales people told me that but I assumed that was BS to get my money, but he assures me that they did a lot of testing on them and it's a good idea to replace once every 5 years.

The other interesting thing, I have an internal blow off plumbed back into the turbo inlet. I tried an external one and it ran rich and like a do until high revs, he had the answer, the MX5 ECU/AFM on the NB use averaging so if you dump out a bunch of air from the blow off the system still thinks it's gone into the motor so keeps the fuel rich.