MFI throttle bodies - Eurometrix getting a call tomorrow!

[jkeyzer]

Hello again -

I am finally giving in and calling up Eurometrix tomorrow to see about having my MFI throttle bodies rebuilt.

Symptoms are: car idles very poorly when the engine is hot (approx 100 deg C) and has been driven for an hour or two (esp. during the day). If I drive at night or short distances and only get engine temps of 80 deg, the problem is much less severe and I only have intermittent idle problems (seems to vary from stop light to stop light sometimes). Problem has existed in some form since I bought the car in August and I have replaced most ignition components (except distributor itself). I have been tweaking MFI for a couple months now.

Car runs very, very well except for idle problems. LOTS of fun to drive when I don't have to come to a stop often!

In the past I have attributed this to incorrect mixture, but the thermostat seems to be extending properly. I think what happens is that when I have the idle problems, opening up the throttle valves (disconnected pump) sometimes speeds up and smoothes out the idle, and this is what I am incorrectly diagnosing as a too-rich condition. Instead my theory is that this is simply making the correlation better between cylinders (percentage error from leaks becomes smaller).

If I spray starting fluid or propane around the base of throttle body stack #1 the engine RPM changes, but only when the engine is very warm and experiencing problems. I replaced gaskets and cleaned everything thoroughly so I do not think gaskets are the problem.

Sounds like a hairline fracture or leaky bushing, right?

We'll see what Matt @ Eurometrix says. If this will fix things I am willing to spend the big bucks. I want my motor to be happy (and then I will be too!!!)

[FA-18C]

Jeff
CAn you forward and info you get on pricing and turn-around? Just to store in my info file for future possible costs..Thanks

[NYSCAR]

I'd like to hear about prices and any info you uncover myself. I'm in the same boat as you, Jeff. Wierd idle problems when the car has been running for 45+ minutes.

Brad

[jkeyzer]

Brad - Very interesting... So I am not alone. Do you think it is something more than a mixture problem in your case?

I talked to Matt this morning, and he is a very nice guy and willing to give advice without me buying into a rebuild yet.

His suggestions were as I have heard before, and one new one... Check for lateral movement in the bushings esp. up and down, check for grooves in the bores, and here's a new one, check for flatness of the base to make sure it is not bowed and causing leaks between the TBs and the head.

Price looks like it will be around $600 depending on whether the bodies need to be bored out or not.

[kwikt 911]

I had my tb's rebuilt by Eurometrix and must say I was very pleased with Matt's work.

[jkeyzer]

kwikt - I have been told his work is very good in the past by several people.

How did you determine yours needed rebuilt?

Today I tried to reproduce the problem and wasn't able to get the RPMs to change reliably no matter how much carb cleaner I sprayed at the bases. I tried a different method of adjusting the throttle plates this time and drove around an hour with a fairly good idle, but the temp never got above 90 deg. It seems like the real problems start when I get up to 100 deg or so.

[kwikt 911]

Well in my case the throttle shafts were loose thus causing an air leak. Also the butterflies would'nt seat properly no matter how I adjusted the stop scews then the correlation would be out of wack. Matt replaced all the bushings, installed new butterflies, bench flowed them, new linkage and throttlle stops, and finally powder coated them.



Kevin Kipta
72 911T/E

[jkeyzer]

Kevin - How could you tell the butterflies were not seating correctly? I may have a similar problem but I don't think the air shafts are leaking much although a couple bushings do have some wiggle up and down. Very minor but maybe enough to cause problems. I do have trouble getting rid of all the popping and shuddering at idle.

In your experience how does the idle mixture affect the idle speed/smoothness? Is it possible to foul plugs with too rich an idle speed mixture and cause a cylinder to start misfiring? Any comments from other board members?

I didn't know Matt powder coated everything. That's neat.


I am still undecided where the problem lies here. Today I leaned out the idle mixture a LOT (couple turns) and was able to restore a good idle at high temps... Seemed like so much fuel was going to the engine that one or two cylinders weren't firing regularly.

One interesting thing I see happening is that the microswitch will tend to resist the pump going all the way back to its idle position and this will sometimes make a richness problem even worse. The butterflies will go all the way closed because they have stiffer springs and there is some slop in the linkages.

Thanks for the info.

[jkeyzer]

Here's an interesting discovery... Opinions please!

If I pull the vacuum line to the distributor (and plug the end of the vacuum hose) the engine speeds up but it is accompanied by a very bad, repetitive misfire. Fast thumpthumpthumpthump sort of thing.
I am not sure if it always does this or just when it is running poorly.

That's odd, isn't it?

What are the symptoms of a failing fuel injector?

[Paul Thomas]

Matt does indeed do very good work, and he is willing to give advice freely even if you haven't writen him a check.

Someone mentioned turnaround, he had mine for about a month and when i go them back i bolted them up and my idle is now smooth as glass. I had a bad miss at idle and the stacks were impossible to correlate.

FYI: He doesn't powdercoat the throttle bodies, he uses Plasticoat Black paint. I think it's #230.