Have had a rough idle for 2 years--1992 firebird--2 places told me it was the fuel injectors--needed new ones--I took it back to a mechanic who is an mechanical engineer--he said he was sure it was a valve problem and gave me the option of changing or not changing the injectors-he found an oil leak and did a total valve job and other maintenance things--drove it over 800 miles--still drives great on the highway but does not idle smoothly --I am guessing that the injectors are still causing that problem???

There are several signs that can indicate a malfunctioning injector pump on a Toyota LN166. The most common sign is the engine struggling to start and running rough even after the engine has warmed up. Other signs could include uneven power delivery, excessive smoke from the exhaust, and hesitation or stalling when accelerating. To diagnose the problem, you should check the fuel pressure, the fuel filter, and the spark plug for blockages or signs of fouling. Additionally, you can check the injector pump for any signs of wear or damage. If you need further assistance, you can consult a certified Toyota mechanic for further diagnosis and repair.

How long since a tune-up? Include air filter, fuel filter, gas injector cleaner...Also check the Idle Air Control valve on your 3.4 V-6...It can be dirty or clogged over time...Located on the air intake plenum...your auto parts store can also show you a diagram...Fuel pressure must be constant also, your Firebird is worth having the fuel pressure regulator checked, as well as the fuel pump...

Could be the injectors. You would need to figure out which cylinder is weak, and then why. Have you replaced the fuel filter in the past 12 months ?

The reason for the problem can be faulty fuel injectors, clogged air filter, faulty ignition coil, and many more or none of these. These are just assumptions for the problem. The real problem may be something else, so I would suggest you to get your ride checked for the error code and then update your answer indicating error code.

On your car the ECM is set up with two quad injector firing sequence. All even numbers and all odd numbers. It is rare that both would go out at the same time. The ECM grounds the injectors, so I would check for power going to the injectors first. This could be a fuse or a bad wire. One wire feeds power to the injectors until it reaches the engine. this is a start, so let me know. Randy

I was having a similar problem with my 2002 Envoy. Usually when accelerating at 60 and 90km/h it would have almost like a clunk and idled rough.

I took it into the shop and they said a tune up would be the first step to correct the misfire (25 options to choose from!) After pulling the spark plugs the 5th and 6th didn't look right. As a result my mechanic ran a compression test.

The 6th cylinder is only putting out 80lbs of pressure where as the rest were putting out 195lbs (factory says it should be around 215lbs). His recomendation was new motor or new vehicle.

A 2002 is not an "older car".
You should easily be able to get 15 years out of any decent car.

But the PCM and TCM are not likely bad.

First start with a simple tuneup, with plugs, wires, etc.
Then you try diagnostics on the fuel injection, such as temp, O2, and air mass sensors, as well as filter, fuel pressure, etc.
Then check things like ERG valve, fuel vapor purge valve, etc.

The last thing you do is give up and buy new control modules.

look at spark plug 6 see if it is foul out with oil. when you first start you car up and it smokes blue you have leaking valve seals and stop up oil return holes.if all is good .check 6 injector make sure its getting power.

maybe it is the ignition modual.

There is a little tester calles a NOID, it plugs into the harness connector to the fuel injector and flashes if there is a signal, they only cost a few dollars.