Stumble/lack of power between idle and 4200 rpm on 1.6L DOHC

[willypete]

But here's the catch: only once the engine has warmed up does this occur.

Symptoms: I can depress the gas pedal ~25% before the engine bogs down between idle and ~4200 rpm. This only happens once the engine is heating up/at operating temperature, however. Once above 4200 rpm, the car responds normally. Also, once warm, the car is incredibly hard to start; requires much cranking, and sometimes an application of starting fluid (which I don't know whether or not is harmful to the electronic components in the intake).

So far, I've replaced the MAS (~4.8 ohm on the intake air temp sensor vs. ~2.4 ohm), and am going to replace the O2 sensor tomorrow (reading 8.6 ohms vs. 6 ohms spec @ 68F).

I've also checked out the throttle position sensor per the FSM, as well as the EGR valve. These are within operating spec. I have checked the resistances of my plug wires (16Kohm per meter, iirc) and they spec OK. Plugs themselves are fairly new (<5,000 miles), as is the dizzy cap. Fuel and air filters are brand new. I have inspected the air inlet lines, and can find to cracks or holes.

Things I haven't done, but am thinking about: jumpering GND and TEN connectors on the test port while @ operating temp, testing the fuel rail inlet line pressure, testing resistances of the fuel injectors.

Nothing I've done has alleviated my problem. Does anyone know which sensor the ECU takes a reading from between those RPM ranges (or thereabouts) and at operating temperature? That, or the ECU itself, is the likely culprit, IMO.

Any help would be greatly appreciated.

edit: Also, there is no check engine light illuminated during any of these conditions. I have verified that the CEL does work, so it's not a burnt out bulb.

[Ryan]

I read first sentence only, and I say "DISTRIBUTOR!"

Edit, I read the rest, and I still say "DISTRIBUTOR!"

[willypete]

Are there any tests I can do to eliminate individual components or pinpoint something? Everything I've read in the FSM suggests that I need to have a cast gold, diamond studded, platinum-plated contact magicounobtainium testing module to figure the dizzy out.

I like to figure out how stuff works, in addition to fixing it

Or should I just replace the whole thing from the cam gear up and call it good?

[KL01 FrEaK]

replace the whole thing, i had the same problem on my DE, these dizzys r weak and fragile, they do their job, but a bit more quality in the build process of its internal coil wouldve been greatly appreciated, my buddy with a ZE Probe GT has been thru 4 dizzys in the past 2 years(wtf) i know right

[willypete]

Just got back from poking around the distributor, and the resistance readings are all jacked up; one is way too high, and the other is non-existent. The new distributor is on order and should arrive in the next few days. Hopefully that will be the extent of my problems for a while.

Thank you for pointing me in the right direction

[willypete]

Popped the new distributor in today, set the timing, and all is well!

Thanks again for the help