Help with analyzing compression readings ???

Help, I'm a little confused here....
working on a 1992 Chevy Lumina APV minivan 3.1 Engine
The temperature normally is about 185 - 195 degrees,, and idles at about 775 rpm
without stalling.
Recently my temperature gauge started climbing up to 220 and then dropping back to normal which is a little less than 200. Climbing again to 220 and dropping back to normal again. The engine started running roughly and stalling out when idling at a light.
The thermostat had been replaced... cooling system pressure checked. There are no coolent leaks..
No water in oil, no oil in water. Nothing coming out the tailpipe.
No error codes have been set. An ODBI scan shows all sensors to be operating normal.... however it did note temperature increases to about 220 degrees ( normal running temperature was about 185 - 195 range. )
I put an inductive timing light on all spark plug wires. Looks as if all plugs are firing pretty evenly.... light stobes pretty evenly, no drop outs.
Pulled the plugs out of the front 3 cylinders...all look normal no deposits or white. Ran a compression test on one head with a screw in tester...
cyl # 2 read 150 cyl # 4     read 165 cyl # 6 read 190 lbs
I have a Helms Service manual which (surprisingly did not give an expected compression value. However it does state that the weakest reading should be at least 70 percent of the strongest and a minumum of 100 lbs.
Could not check the rear cylinders because of the diffculty of access.
Squirting about 1 tablespoon of oil into cylinder #2 brought the cylinder reading up...Not only in #2 but also in adjacent #4.
Is this indicative of a blown head gasket between adjacent cylinders 2 and 4 ??
Is there anything else that should be checked to complete the diagnosis ???
Thanking you in advance for your help !!!
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I don't think compression is your problem here, if the running rough and stalling was caused by an internal engine problem, it would show up at higher driving/engine speeds also. Look for vacuum leaks particularly around the throttle body gasket, also check the egr for not seating, 2 common problems.

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how about the timing? you mentioned using a timing light ,, but is th
timing right on the mark? have you done a vaccume test in the engin while running?a vac gauge hooked to the engine can be a good indicato of what your problem might be
is the thermostat opening at the right time , sure it has been replace , but ive had brand new thermostats right out of the box that didnt wor right , id test it in boiling water with a thermometer. is the fa electric on that vehicle or is it the old thermal clutch type? i can remember which type it is....(and i dont feel like getting up an looking it up in my motor manual. )
is the spark hot enough? sure it is sparking , but is the spark weak?
as for the error codes , there wernt that many codes in 92 ( 50ish if remember ), not like today whre they can practicly show you the proble down to a wire on some cars
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Still working on the problem..... but at least I'm not fixated on the head gasket being defective. Never had a head gasket go bad before so not sure what the symptoms are.
Checked system vacuum 21 steady no flucutations.
Egr valve seems to be working okay. Tested vacuum at the EGR valve regulator.... manifold vacuum was there. nothing was passing through till I grounded the diagnostic terminal, then vacuum passed.
I used a handheld vacuum pump to test the EGR valve. Works smoothly. Removed it anyway and examined the EGR intake manifold port. No carbon. Clean what little carbon was on the valve and replaced. Retested.
Checked engine timing...with the EST disabled. it was retarded by a good 10 degrees or so before the timing mark plate. (specs call for 10btc). The actual reading was so far retarded that it was about 1" before the plate. I had to recheck several times just to make sure the light was on #1 cylinder. (Yup it was). Distributor hold down clamp was was tight and no ignition components had been replaced since last year....when ignition timing was set. Not a good sign, is it for the timing to move that much. The 3.1's use a timing chain rather than a belt so I guess I'll keep a close eye on the timing to see if it changes anymore. Do chains jump ??
Anyway, engine temperature is still up about 205 degrees (using a OBDI scan tool) but seems to be steady. I'll keep the scan tool connected for the next few days.
Most of the OBDI Codes are senor related. MAF, Idle Air, TPS, O2, Battery, Cooling, Rich/ Lean, Closed/ Open system. The ECU is definately controlling the system. Mixture is crossing rich / lean.
Took the car out for a spin, still running well at highway speeds, I didn't hit enough lights to see if it would stall, but it ran in the driveway for about 15 minutes without a burp.
Well, that was my two days off...gotta head back to work tonight and won't have a chance to look at the car again til next week.
Thanks all for your help.... if anything else comes to mind please let me know !!
Thanks Again !!!
Peter
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btw..... engine only has 96, 000 miles on it. My previous Lumina went to about 185,000 miles so I've got a lot of faith in the 3.1L. Usually they are good engines, (cept for the oil leak and a few other minor defects).

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Peter how is it this engine has a distributor?

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It has a distributor. No doubt about it.... Also has a TBI - Throttle Body Injection.... I know that in later years GM went right to port injection, but this one still has distributor (rotor, cap etc) and a TBI. Then again I haven't looked at a lot of later model years...but had two 92's and both had distributtors.
You seem surprised ??? I wonder if this was a transition period ???
Peter

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Interesting that your 3.1 had TBI and a distributor. My 92 Lumina Euro 3.1 has no distributor and individual injectors. Roy

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