350 TBI roadmonster running rough when warm

1992 buick roadmaster 350 TBI 118k miles.

couple weeks ago i went out to pick the kids up. got to grandma's house 10 minutes away and as i pulled in the driveway the car idled with a noticeable shake. when i went to pull out to leave it sputtered and tried to die under all but the lightest throttle pressure. i had to baby it the whole way home to get here, and it stalled once at a light.

left it alone because it's too cold out. i started it to move the other day and it ran perfect with all throttle input for about 2 minutes. this morning same deal, couple minutes of running great allowing me to move the car and back it up on the ramps then a flip is switched and it runs rough and stumbles.

today it's about 30 so i threw on my long johns and crawled under the car and swapped out the fuel pump, because i figured it could be it but moreso because the car sat for about a year prior to me buying it a few months ago and in my experience once a gm pump sits a long time it's only a matter of time before it pukes. the sock on the pump was falling apart. i was optimistic at that point, but once i got the tank back up and the filter changed, i fired it up and it still runs rough.

i have pulled the air cleaner and verified nice cone of spray from both injectors. crack open the throttle by hand and it tries to die. i have no check engine light(obd1 is not smart like obd2 that'll throw you a code if you sneeze wrong).

i have had literally a bazillion TBI gm vehicles thus far, however i've never had one do this. i had the ignition module thought, but i do not want to just start throwing parts at the problem until it goes away.

Bad coolant temp sensor?

EGR valve sticking open?

temp sensor first on list to test. when i unplugged it when car running the idle dropped. waiting for engine to cool so i can pull it without getting burned to bring inside to test.

egr - looks like it has a vacuum one so i'll get out the mityvac and see if it opens and closes or does nothing.

keep thoughts coming and i'll keep testing things

My first thought is an egr not closing fully. Had a few do that. Pull it and clean it if it holds vacuum.

Even though its not OBD II, one should be able to pull some codes. I doubt Autozone of Advance can do it with the readers they have.

I had a somewhat similar episode with my Nissan truck after I rebuilt the engine and ended up replacing the TPS and air flow meter. Between those two, the problem went away. It also has TBI injection.

Should be able to pull codes via the paper clip method on that era GM, There are two terminals that you jump at the diagnostic plug under the dash. Based on my experience with TBI I believe you have a bad MAP sensor. I grabbed a few out of the junkyard to keep from buying new aftermarket ones, the GM/Delco ones usually last almost forever, I wouldn't be surprised if it's the original.

no codes. i have an actron reader for obd1 gm. it's a glorified paper clip in a nice plastic housing.

i pulled the EGR and put vacuum to it, nothing moves. i put my mouth to the vacuum hose and drew through it, and could hear air leaking in. mityvac with good seal won't hold any vacuum on it. diaphragm bad? stuck open? it looks like crap

have coolant sensor in house warming up to room temp so i can test it at room temp and in hot water.

have a drawer full of known good map sensors so that's an easy swap out part.

Diaphram bad.

Not worth 60 bucks when you don't have inspected. Build a block off plate and see what happens.

thats the plan for now. car has to pass one more emissions test in july 2016 then it will be exempt. if the blockoff works, i'll put a new valve on when it's not 30, dropping fast, and starting to snow.

what about idle control valve?

threw on known good CTS and MAP. blocked off egr. cranking with the starter it sounds like it's trying to launch something out the oil pan. fast, slam stopped, slow, fast, stop. it started , and once started there is nothing banging around but it's still running poor and trying to stall, and i got backfire with actual fire out the throttle body trying to rev it.

the horrible cranking reminds me of trying to start something that the timing is severely off in.

going to let it sit a bit and see if i can start it and check timing. not sure if that could even be an issue that something could fail and make the timing be off

it sounds horrible trying to start it. i can hear the starter turn 3 times and then stop(hard enough to make car move when it slams stopped), over and over. no start, killed battery trying. i can almost swear when it started earlier i had some connecting rod type noise that went away after a couple minutes. it's always had some very light tap tap noise. i've put about 1500 miles on it for $800, need to get more out of it.

kill it with fire? throw the 350 in the "hey that didn't work" pile and put in a 454 and bring it to the challenge?

Check to see if the distributor has play in the shaft. Those distributors are bad about wearing out the top bushing. Probably not the problem but worth checking.

Try a new distributor cap.

Ugh, hope you didn't have an intake manifold gasket fail. Sounds like you could have hydrolocked the engine somehow. Pull the plugs and check for fluid where it shouldn't be (moist spark plugs). Unless the timing chain broke or the distributor gear is stripped or the hold down is loose your timing should be ok. A big block B-body sounds like lots of fun!

Yeah, I'm in the timing camp here. Check the dist. to make sure it's firing on #1 when it should be. Might be time to pull the timing cover...

dropped from 32 to 12, not pulling anything right now. will charge battery back up and the timing light is already in the front seat ready to check that if it'll start. if timing is off, i may have to inspect timing chain. not sure when they stopped using nylon teeth on the cam gear but i had that happen to an older engine.

today, after sitting for a week, car starts perfect cold, then does same thing. few minutes in, runs rough, stumbles, stalls and barely restarts.

change anyone's idea? i'm leaning toward throwing an ignition module, cap, rotor, and wires at it. it feels perfect cold. revs quick, no stumbles, can put in gear and put foot down and car just goes.

Ignition module sounds right, aren't they a known problem? It was my first thought before I even started reading. I guess it could act up in such a way to fire way early and cause your hard stop problem. You'd probably notice the coolant dropping if the intake gaskets were bad enough to cause a hydrolock.

No familiarity with the GM TBI, but is there a cold start injector or something that's sticking on making it run fine cold, but uber-rich once it starts warming up?

Tried starting with the IAT unplugged? I believe the car has one.

Seems very weird that it'd be connected to temp. Makes me think ECU is causing this based on it's idea of what some temperature is, like the intake air or coolant.

Wonder what a different ECU would do... but that's definitely throwing parts at the problem without even a decent theory. Family had a 1989 Olds Delta 88, so different I know, but over 235,000 miles the car got 4 computers installed. Would last for 60k to 80k, then run odd, and the dealer would swap the ECU and the car would be fine again. Seems very weird now.

What's the fuel pressure doing? Imwondering uf pump is dying. Or the regulator.

Id also reccomend making an aldl cable and getting winaldl. See all tbe sensir data

pressure 13 constant. new pump/filter as i automatically went to the "this is common tbi fuel pump death stuff" and changed it. injectors spray perfect, beautiful cone pattern, no drop in pressure. i'm so TBI that i have the dedicated tbi pressure tester, i've just never had this before.