1990 w/2.5L 4cyl - random rough running

My car is back again (LOL). It is a sedan with the 2.5L 4cyl with approx 227,000 miles on it now. Just fixed a severe oil leak that turned out to be the valve cover gasket thankfully. I am proud to say it does not leak nor burn any oil and it doesnt lose any coolant fluid either. Last time I checked I got a phenominal 29 MPG with this car which wasnt long ago I checked.

Here is what I have doe so far. Replaced crank position sensor, ICM, both coil packs, all plug wires and plugs (bosch platinum +2), throttle position sensor, air/fuel mix sensor, virutally all the vacuum lines except those that are still good but will be replaced soon as well. Flushed radiator when I replaced intake manifold gasket, shaved manifold to get truer fit as it was ever so slightly warped anyway, replaced tbi gasket, replaced egr gasket. I checked egr and it functions quite well still, replaced fuel line gaskets. Replaced the broken thermostat with a 195 temp thermostat.

Here is what it is doing - Cold, starts great, gets going ok with a few stutters or misfires it feels like. Once engine warms up idle is a bit rough, acceleration is quite smooth and feels great until I get to 45 ot higher MPH. That is when the locking torque convertor kicks in if it has one. If it duz not, I have a 4 speed auto tranny. Sometimes it will run mostly smooth but other times it runs very rough at this speed.

I think I covered everything - if you need to know more to help, lemme know and I can tell you more

Sounds like ignition. Have you replaced the plug wires and plugs? Sounds like the spark wants to find the shortest path is that intermittent miss.

thats what I thot as well - yes, I have replaced the plug wires when I replaced the ICM, coil packs and plugs all at the same time - the intermittent miss, as we will call it, didnt go away when I replaced all these items with brand new items last year when I had to do the ICM - I used 7mm wires as I cant find 8mm wires for my car that will fit it

I dont have any sensors showing when I use the flash code - I have not replaced the map sensor nor the idle air control valve yet - it cud be something is making them not run good but good enough to not show a code is what I am thinking - I dunno really as this is all new to me still - I am used to cars from the 70s and before

Make sure you don't have a simple wiring problem on that TBI...sometimes a bad ground or wire will make the injector break up....

Try fiddling with the TBI's wiring harness all the way to the injector while it idles, see if you can get a stumble or stall out of it...

Seems you answered my question. How about two more things more or less a shot in the dark... literally.

You have a bottle mister? Take that mist bottle, turn the lights off in the garage, start the car; mist spray the coil wires; see if there is a spark the water can sent to ground is like you are making a cloud over the wires. Not literally, but so the mist has that "miss" path to follow.

The other one is take the ground strap, scrape new metal so as to expose the body metal. Then, same time, scrape or file the ground strap to frame using the same , "find bare metal" so you have a good ground source.

Next would be is to push the car out of the garage and let it cool off. Next is to start the car, then spray the intake manifold or any intake track that uses the intake manifold for an air source. Could be an air leak if not a spark leak... Darn, these misses are hard to pinpoint.

ok, didnt do the spark plug wire thing as I dont have a garage so I will just have to wait until its dark - I did shake the wire harness from as low as I cud get to the injector and no change in the way the engine ran - I think I will do what I can to find a premium set of spark plug wires in 8 mm size and begin there - that wont happen until wednesday though cuz that is when I get paid next

as a side note, is there somewhere online that can help me with making valve adjustments properly?

Sure. Right here. You do not need to set the valves at TDC. You can remember this as you set the valves. Use the term, EOIC... That means, you watch and then you stop as soon as you see the other valve do it's thing; you are ready to set the other valve.

So, lets say you have the EO = Exhaust (just begins to) OPEN! You then stop right there and set your intake valve. Then you watch for the IC = Intake CLOSING and then stop immediately once you see the intake JUST BEGIN to close, (being as soon as the EO event is the same practice).

This is where you are at the highest point on one valve and the lowest point on the other. This is an old trick still used today by the NASCAR boys who build engines. So, you want precision, you set the valves not at top dead center like the book says. You now know the universal trick for any engine with a cam now is the EOIC method.

Next is to use the G0-NO-G0 System. Say you have a valve set at .003" clearance for argument sake. Now the go-no-go works as this example by inserting a .002" feeler gauge is the GO! This is because you are not tighter that .002"... So, you would then insert a size .004" feeler to make sure you are not wider than you book number they call for. This qunatifies you are no wider than .004" using that size feeler is the, NO-go entry.

You would not believe that slight gap difference would do to your performance using these two tricks. Hope you understood what you are attempting on the valve train action. It is very percise and you do not bend feeler gauges. The drag is butter smooth. Say, you want that .002" but really it is .002444485858696 or something like that. Meaning, it is way less than 2.5. Therefore your feeler gauge should be as new looking and not bent where you pushed and bent the feeler gauge into a gap that is, .0018888899999, and not .002"... You sorta see where you could bend a blade and you would still be more or less on the money is splitting hairs.

Same as a SB Chevy V8...start engine, tighten until engine idle reacts, go back 1/4 turn, done.