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Poor Running
Posted by Ramblerdrver (more from Ramblerdrver) on Fri, 23 Aug 2002 15:56:38
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I'm looking for some expertise/experience in diagnosing what's causing my 
daughter's 1988 900S with A/T nad 220k miles to run poorly. Unfortunately 
it's a bit hard to describe the symptoms. It starts fine cold and hot, altho 
once in a while it will start and die a couple times when hot. When you 
'goose' the throttle in neutral, the engine accelerates like it's missing on 
a cylinder., but smooths out at steady rpm. Gets better as engine warms up. 
In gear and taking off from a stand still, the engine seems to miss a beat or 
three. Daughter says it seems worse when it's humid or rainy out. 

So far here's what I've looked at and done...w/o improvement. Installed new 
plugs, plug wires, and rotor, altho they all looked/measured good (except as 
noted below). Fuel pressure ok. Fuel injectors look as clean as new. Fuel 
injectors 'click' and resistance correct and voltage to injectors is correct 
and increases with rpm and opening throttle quickly. Injector o-rings 
replaced. Spark appears strong. Signal from Hall sensor to EZK control module 
correct. Engine temp sensor reading correctly both at sensor and at LH ECU.. 
No vacuum leaks at hoses. O2 sensor giving proper output signal. Air mass 
meter 'burn off' cycle operating. Compression pressure was 170-200. Timing 
chain tight and came in proper time. 

I only found two questionable things...the plugs in cylinders 3&4 seem a bit 
cleaner than 1&2. The ignition timing at idle was 9 instead of the 14 it 
should have been and the advance seemed erratic. I reset the timing to 14, 
but this didn't help the erratic running. 

As a result of the timing being off I replaced the EZK control module with 
another used one...no help. 

So...any other suggestions? Is there a common problem with the EZK modules 
that would result in both these units having the same problem (a 'new' one is 
$500+ !!)? Could the air-mass meter be going bad, even tho it appears to be 
OK? Could there be a wire somewhere that's 'shorting out', especially when 
air is humid or wet? Replacing the air-mass meter and/or LH ECU may have to 
be tried, but doing so gets expensive since they may not be returnable if 
they aren't the cause. 

Thanks for any help you can provide!!
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