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Rough Idle Stalling issue 1995 Firebird 3.4

3836 Views 9 Replies 6 Participants Last post by  Injuneer
I will be the first to admit im not mechanically inclined but the past few months my 95 Firebird has taught me alot, so I apologize in advance for not understanding alot of terms and lacking knowledge of cars engines and mechanic basics. But I have had a rough idle issue, it idles rough from a cold start and even when warmed up, once i get over 55 mph it does great, I replaced fuel filter,Mass Air flow relay sensor, fuel pump is fine, we did the EGR delete, learned of the small two inch hose in the fuel tank that goes after so many years and get in the tank and no hose! help please any advice would be awesome! thank you very much
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Is the SES light on? Have you checked the condition of the spark plugs and wiring? Have you attempted to use a scanner that can read your car's trouble codes (not easy to find these)? Not all trouble codes will light the SES lamp.
Yeah I'd agree with ^^^^ when I had that in my old Grand Am it was the coil packs going bad. Check codes!!!!

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Yes spark plugs and wiring are ok, we reset the code thing(i do apologize for not knowing what all the parts are called im still learning, slowly) when we did the EGR delete so it wouldnt give error codes because the EGR was gone, ( i think im saying it right) the SES light is on, I have had a few friends try and do the trouble code but they didnt have the right scanner they said , but do all cars have the small rummber hose in the fuel tank, we dropped the tank and there is no rubber hose, i have come to the realizationthat the more I learn the less I kno thank you for helping, im at a loss with it all

Yes I guess there is more than one coil and we replaced one (why i dont know my friends are helping me not sure how much they help but hey, A for effort) I will have to get the rest done
Also it has been mentioned to me something about the ignition module could be the problem? is this at all possible , i have not the slightest clue what it is, gonna do more research
You really need to get the trouble codes read. There are two way to do that.

The first is a handheld scanner like this one:

With that scanner, for your 95, you would also need an AC-12vDC adapter. You can either buy the OBD1/power kit for about $35 more or just find an adapter by itself for about $5. Since they are very common, you may already have one for something else.

The second method requires you to have a pc that can be placed within cables' length of the car's OBD1 socket. Buy a cable for about $60 and use my free scan program, "Scan9495-V6". The advantage of using this method is that you can also datalog/record the engine data while the car is running and driving, so that we can help more with this.
I also suggest you use the link I provided to download the 95 service manual. You will learn much by reading it.

Also go to your public library, most have an automotive section. Get books on auto electrics, auto electronics, fuel injection, and computer controlled systems.

If your going work on a car from the 80's on, this is information that you need to know.
Sorry your having issues, but a scanner may or may not point you in the right direction. The scanner I have (works without any tricks) is the Actron CP9185 Elite Auto Scanner Code. Unfortunately on the 95 (not quite OBDI or OBDII, there are no sensors that will read plugs/wires or coils (so you won't get a code thrown for those). So the scanner will be a good start to eliminate things before starting to rip them out. So for your issue, it could be lots of things - O2 sensor(s), clogged EGR tube (not sure what you removed in addition to the EGR), a PCM problem, IAC, maybe a vacuum leak. What does it do while your below 55 (backfire, no power)?
You mean a scanner like the one in my first link? ;-) I stand corrected about the 95 needing a power source, It does have the 12v at the DLC, so no power adapter is required.

The OP does have a lit SES indicator so there is a code for something.
Do the scan. It is worth it. There is no complication with 95 being not quite OBD-1 or OBD-2, other than the DLC having 16 pins. The PCM is totally OBD-1 and identical to the one used in 1994. It can be scanned with an OBD-1 scanner using a 12-pin -> 16-pin adapter, or using short jumper wires:

This indicates 95 LT1. but the 3.4L DLC is identical

Not likely to be the fuel system if the system is capable of adequately supplying the required fuel above 55 MPH. The only hose in the tank is the corrugated, clear plastic flex line that connects the pump to the support unit. They can leak, but not a typical problem. And the problem would show up more as the load on the engine increases.

Rough idle could be due to improperly eliminating the EGR valve. You should have multiple codes (DTC 75, 76, 77) for it being missing. Resetting the PCM does not eliminate the diagnostic that produces the codes. The PCM would have to be reprogrammed. Other than the expense of the valve, there is not much to be gained by removing EGR. It actually helps reduce the chance of knock (detonation) when lugging the engine at low RPM. Typically, EGR does not operate at idle. So that may be the source of a vacuum leak.

As noted above, look at the possibility of plug and wire problems, vacuum leaks, leaking injectors.

A data log, using GaryDoug's 3.4L V6 scan software may uncover some issues. That allows us to look at the long term fuel corrections, for example, which may tie in to the specific problems causing the misfires.
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