I recently bought a 99' Impreza outback sport. The check engine light was on when I bought it and knew I would be putting in some time working on it. When I checked the codes they came up tps, and cylinder one misfire. Which I knew of the miss from the get go from a rough idle. I proceeded to give it one helluva tune up. When I popped the plug boots out I discover the seals were rock hard and leaking a bit of oil in the plug sockets. So of course I replaced the valve cover gaskets and plug seals. While inside I checked the valves play and discovered that exhaust side of cylinder one was tight and had no play. So I adjusted it as needed. I then proceeded to put iridium plugs NGK wires and a coil pack on, along with a new TPS sensor and both oxygen sensors. The car ran amazingly for a day or so. Then all of a sudden at a red light at idle, it dropped a bit , stuttered and the check engine light came on once again. I put the computer to it and it told me again it was cylinder one misfire. The only thing I can think of is a bad injector, valves, or a vacuum leak some where. I went over the vacuum lines pretty well though and wouldn't think that would be the problem. I was wondering about the IACV motor. Usually when a IACV motor goes out in other cars the engine goes from idle to high rpms then back to idle and is constantly doing that while the car is sitting running. Has anyone here ever have this problem? Or anyone have a problem with a IACV motor that made the car fluxuate down in rpm instead of increase? Its only at idle and runs fantastic and fires on all 4's by the end of shifting out of 1st gear. Also there is plenty of spark to the cylinder. 

When you installed the tps, did you adjust so that it idles corectly?

Large IAC to intake hose on securely?

Check egr valve hose to the BPT.

None of these will give a misfire code tho.

Make sure  plug is securely in socket,

Move wire from 1 to 2 and see if misfire follows.

All I can think of.

 

O.

I used my voltage meter and adjusted the idle to the correct rpms. I just cleaned the IACV and intake with seafoam, which only accomplished smoking out my neighbors lol. I'll try moving the wire now, I didn't think about that. I cleaned the pcv as well, I guess that could be shot. Other than that I guess i'm going to have to get injectors and try that. On the bright side if it is a valve, I'll do them all and have nice rebuilt heads and gaskets.

Welcome to the USMB.

 

A missfire on one cylinder is almost always mechanical (NOT a sensor, wire, plug, or anything easy).

 

Compression check?

 

Often times folks break a timing belt, hang a new belt and drive or sell the car and if they were lucky enough not to bent the valves bad to begin with they don't do well for long.

 

I assume this is a 2.2 being an Impreza Sport.

Yep it's the 2.2L, and I could see that being the case. So I assume my best bet would be to do a overhaul on the heads? 

Do compression and leak down tests before pulling heads.

 

Low speed misfire is usually a spark plug or wire issue. Could be injector related, got any BG 44k?

Yea that"s what I was going to do. I'll have to rent the compression tester from the parts store. I don't have any BG 44k, I'm sure that would do a better job than the seafoam and lucas products I've been using. I know the dealerships have it, but i'm not sure where to get it besides them. Maybe ebay will have some.

Compression and especially leakdown should tell a lot.

 

I put off pulling an engine apart because when I do - I do everything but crack the case and do it all right.

 

Often it's easier and cheaper to just find another 2.2.  That 99 is a little werid - but may be able to be overcome.  I have one here and it's the only engine I have not marked with it's problem or miles.

plugs and wires first. this is the most common cause.

imho, plugs and wires cause more misfires than all other things combined.

 

move the wire to a different cylinder. see if the mis moves.

That's the thing, iridium plugs, ngk wires, and coil pack, all brand new, all sparking hard. I can reset the computer, run a few hours with no codes thrown, then all of a sudden at stops, at idle, it fluctuates down to around 550-600 rpms and then back to normal. This is when the misfire code for cylinder 1 is thrown. You would think it would be either air or fuel related. I'm for sure going to do a compression test and a leak down. It just has me stumped to be honest. I have a lot of new sensors I've put on as well, just as precautionary maintenance. 

The only sensors/electric parts on the engine that should affect idle speed are the coolant temp sensor and the idle control valve.

If you have a scanner that can read live data checking the ECT sensor is easy. It should be close to outside temp in a cold start, and should reach about 180-190 when at operating temp. Really doesn't sound like that's the issue though.

 

There are a few vacuum hoses running under the intake manifold depending on if the car has EGR. The hoses for the evap purge solenoid are under the intake runners on the passenger side. The EGR has a solenoid under the manifold on the drivers side.

Entirely possible the gaskets are bad, or an oring around one of the injectors could be bad. The side feed injectors have a large fuel rail that sits in a large bore in the manifold. Not common for the rail o rings to go bad unless someone removed them before.

Also check the vacuum hoses at the evap canister if its under the hood.

 

The misfire could be causing the low idle but there is usually an electrical reason for an idle speed misfire. Mechanical misfires are generally present up to mid RPM range if timing or valve related.