2.4T engine surging at idle
 

hello

i just picked up my car after its 'winter-hibernation'

no problem wenn the engine is cold, but after it's warmed up,
i noticed the rpm's at idle go from 1000rpm to 1500rpm and back again, and this goes on and on at a steady pace.

what could cause this knowing that all was fine wenn i parked it about 4 months ago?

it's a 2.4 mfi - engine

Thanks for any help!

A searching idle at least on my 2.4 (CIS) was a simple adjustment of the mixture. I do not know about the MFI system, but for CIS it was an issue of lean versus rich and it needed to be richer in my case.

Bob
73.5

Hey Bob, thanks for your reply.

Does any of the mfi-crowd knows for sure before I start messing up my mfi-set up...:)

Could it be just a distributor problem?

regards
Johan

Maybe your throttle butterflies are worn, allowing extra air in around the plates or shafts.

This would cause a high idle, which would go back down once 1500 rpm was reached with the throttle closed if the speed switch and microswitch cutoffs were working properly.

You may have a typically rich MFI mixture that with the extra air would allow the idle to get above 1500 rpm. When the fuel cuts off, it goes down and when 900 rpm is reached, it goes to idle fuel level (too rich in your case)

Just my theory:)

Sounds like mechanical advance is stuck in your distributor. While running pull off the vacuum hose to the distributor and see if any changes. Check the vacuum advance, dwell, and timing.

Kevin

OK, for some reason I can't access the tech articles, but they are here on Pelican. Just go to the main page and look to the left side for the tech articles. "Mechanical Fuel Injection" gives a lot of tips.

That having been said, look first at your micro switch on the left side linkage. It must be working correctly to cancel the circuit that causes the surging. And, yes, worn shaft bushings is a likely cause of this. In a nutshell, you have to be able to get the motor to idle at 900 RPM when hot. If it's over 1300, there's a circuit that kills the fuel delivery if the micro switch is closed. This prevents backfiring on deceleration.

It gets complicated, but once the idle comes down, another circuit allows fuel to be delivered or the car would die every time you came to a stop. These 2 circuits start bouncing back and forth creating the surging problem.

You need to study the info and download "Check, Measure and Adjust," what we refer to as the CMA.

Hey Milt,

You were right!

The micro-switch isn't activated at idle. I pressed it manually and the car idled perfect at around 1000rpm

What could cause this. Are the return springs worn?

Are there any aftermarket 'add on' spring-kits so I can fix this problem without having to rebuilt my stacks at this point?

Johan

You can adjust the little screw that contacts the microswitch. screw it in like tightening an engine valve and that will compensate for a slightly worn spring.