Hi everyone im still trying to figure out why my 93 has a misfire at idle ive done a full tune up plugs, wires, fuel filter , distributor cap rotor, fuel injectors cleaned new catalytic converter new tps checked fuel pressure fuel pressure normal checked vaccum pressure and that was also normal checked injectors also normal idk what it can be please help please and also no DTC codes and car is getting only 10mpg.

Stuck open EGR valve?

It can be that ive changed that 2 times already because the first one was bad and when it stubles at idle it sounds like somethings clogged holding the power in and not letting all the power out

It also has the symptom that when coming to a sop it wants to stall but doesn't yet but i can bet 100 bucks that's what it is

Is your throttle body clean? The bores? The back sides of the throttle plates? Two EGR tubes inside the throttle body?

yes i cleaned them they are spotless HUF

Check again the wires for proper routing. You can also run cylinder balance test through the climate control unit. That procedures disables injectors one after another. If RPM does not change when a particular injector is disabled - you know something is wrong with that cylinder.

ok but u really don't think it's the egr valve

What buttons do I have to press on the climate control to do a cylinder balance test

What buttons do I have to press on the climate control to do a cylinder balance test

I am not familiar with 93 Deville. Can't help.

And wouldn't a fuel pressure test tell me if the injectors were bad?

You have to get into the override mode, but other than that it's been way to long so I can't be of any help without a FSM.
ok but u really don't think it's the egr valve
You could pull the EGR and check and clean the pintle valve. If it is carboned up and not closing completely it could cause these symptoms.

And wouldn't a fuel pressure test tell me if the injectors were bad?
Not likely unless they where leaking like a sieve.

ok ranger i will but wouldn't a fuel pressure test test fuel injectors and fuel pump and all the fuel system?

That will tell you how much fuel pressure you have (how well the pump is working). It won't tell you if you have a bad injector. The injector is electrical. Get a mechanics stethoscope and listen to the rhythmic tick, tick, tick of each injector pulsing. If one is not pulsing you will be able to tell by it's silence. You might be able to use a vacuum hose or a screwdriver in lieu of a stethoscope.

ok im gonna try that tomorrow i hope it's not the injectors

If you can't figure out the cylinder balance test through the computer like others have suggested, you can get the same results doing it the old fashioned way. When the engine is running, pull one plug wire at a time and listen for RPM change. Narrowing down the affected cylinder will be a huge time saver in the end.

If you can't figure out the cylinder balance test through the computer like others have suggested, you can get the same results doing it the old fashioned way. When the engine is running, pull one plug wire at a time and listen for RPM change. Narrowing down the affected cylinder will be a huge time saver in the end.

Yes, it is possible to check that way. The only side effect is that unburned fuel can hurt the cat converter.

Another possibility (often overlooked) is a bad ECM. Cheaper and easier to replace than some other parts you have already replaced.

Yeah and i just put a new cat in 2 weeks ago would a compression test do any good?

ok ill check that i really doubt it's the fuel injectors but im gonna check that tomorrow

just wondering is the ecm the same as the engine computer?

just wondering is the ecm the same as the engine computer?

Yes, "the computer" is known as Engine Control Module (ECM) or Powertrain Control Module (PCM). It is less than $100 at Advance Autoparts.

Sounds to me like it's time for a compression test (that's just me :)) That may tell you something, since you have done many other things so far.

I asked about the compression test because i did that 2 weeks ago and all cylinder were firing evenly and no low compression at all

A compression test will tell you if you have worn rings or a burnt valve. If you did that and all cylinders where close, then that is not the problem.

yep all the cylinders were very close i just really wanna find ot what the problem is i dont want my baby running like this

Also the idle air control actuator is bad would it cause the vehicle to stumble light acceleration once i give it heavy acceleration the stumble goes away checked injectors injectors are good.

You mean the ISC (Idle Speed Control) motor? NO, once the throttle is off idle that does nothing.

oh idk what it is then ive checked fuel injectors today and everything was good

The car only stumbles on acceleration when the car is hot. Not when cold

When the engine is cold, the ECM runs in open loop, which is a richer mixture for start and run until the engine warms up. Sounds like it's running lean after warm-up, which could be a number of things wrong in the fuel delivery system.
I'm not familiar with the port injected models. There must be a pressure regulator in that fuel system somewhere ? Other folks here may know if it has one and where it is.

Yes it has one. It's on the fuel rail.

yeah like i said ive checked the whole fuel system everything is ok.

When's the last time you replaced your O2 Sensors, Because they dont start to work until they get hot. There $20 bucks a piece,there's 2 of them and easy to replace.

Ive changed the like 2 months ago and i only see one where is the other one located at?

I think the 4.9 only had one as I recall.

That's what i thought what else do you think it can be ranger?

The injectors passed the ohm test? That's good news but kind of surprising. I would put some 87 octane in there and run it hard to blow the carbon out of it. It could still be the ECM too like HUF said. I think there are threads here where the ECM cured some quirky problems. I don't remember what the spark plug gap is supposed to be but sometimes GM likes to recommend .080 and that is too wide for any GM car. That's my $.02 of rambling; good luck.

That's what i thought what else do you think it can be ranger?

Not likely, but there is an outside chance that it could be a burnt valve or worn cam lobe. I remember my '92 (4.9) had a very slight miss at idle til the day I traded it at 125K.

It does it very very litle now i put some fuel injector cleaner and we will see what happens and the car is real smooth at idle now that i changed the ISC yesterday

Maybe if you keep adding the injector cleaner when you gas up, the fuel system will get cleaned out OK and you can go from there if the problem persists.

ok im gonna keep doing that and when i started it before it sounded like it was gonna stall but didn't could the catalytic converter have hurt the 02 sensor?

Keep in mind that injector cleaners are strong solvents. More IS NOT better. It will take the insulating varnish off of the windings on the pump and injectors. If you are going to use that stuff, follow the directions.

ok i will i use techron fuel injector cleaner

As an FWI, in the devilles, pre-'94 had one O2 sensor in the front exhaust manifold. '94-'95 had two O2's...

At this point, I would still suspect injectors. While the may have ohm'd out, you still can't be positive they work correctly at all temps and conditions. Just because an injector appears to work correctly at room temp doesn't mean it works at operating temp.

Injectors really hve to be run-tested for flow. Either take them in or replace them cheaply with a used set.

I was wondering could it be that I have autolite spark plugs and wires in the car instead of AC Delco could that be the reason why my car stutters very very little now on light acceleration?

I got autolite double platinum plugs and Napa Belden wires in my 95 deville with a 4.9 and its runs flawless. I think drewsdeville cleared the ignition brand theory up in the (4.5l engine runs rough thread). Here's a link for your injectors
http://www.fiveomotorsport.com/Injector_SetsTPI.asp#caddy

ok thanks and since i put fuel injector cleaner in on monday the car only stutters very little now when i fill up next im gonna put one more bottle of techron baby

On your first post of this thread (mike93) you stated that you cleaned your fuel injectors. Also the Question is did you just buy this car or did you have it for awhile?? If you had it for awhile and this problem just started with your car then you should look at other things then fuel aditives. Here's a link so you can figure out what your (PCM) is reading.
http://myweb.accessus.net/~090/dtcobd1.html

Ive had it for 6 months now the car has been well maintained two months ago i had the trans rebuilt