Stumble backfire snapshift cyl miss rough idle/run

[96qtrip]

HELP! 1996 Q45 = 153K. Rough idle at 750 - pulls hard with some stumble off throttle to 4K then randomly backfires (sounds like its going back towards the filter box) AND surges. In OD and at 45 or greater it can make buttermilk....... symptoms started on highway commute.

codes
P0307 say 7 missfire - but its not a constant miss - comes and goes
sometimes get knock sensor 0325. (Nova ODB2 reader)
had a miss on 3 but found a rat chewed wire to injector and repaired that

checked or replaced --------

camshaft sensor ( driver bank) opened - clean just like brand new)
fuel pressure good per FSM (fuel pump and control module are two years old)
injector cleaner run through tank and engine with 91 octane
Fuel filter replaced
new spark plugs
MAF cleaned - does normal fail mode and recovery when disconnected at idle
IACC operating - good cold start, then starts to miss at idle when warm
found broken intake boot emissions fitings between MAF and throttle body REPLACED large boot
and all attached hoses and clamps
found broken "Y" hose below IACC down to lower pipes at top rear of engine(damn hard to reach) REPLACED "Y" hose. Idle speed adjuster effective
replaced small vac hose driver side fuel rail regulator/damper to manifold
all coil packs will flash my timing light when looped over coil lead in head or in the "wire loop" dvr side

Need some ideas and HELP -- THXXXXXXXXXXXXXXXXXXXXX

[Infinitiguy19]

Are the spark plugs OEM and checked for correct gap[ (Just in case)?

Check the fuel injector resistance (10-14 ohm's) (Or even with all the other injectors if your Volt Ohm Meter isn't that accurate).

Whats the vacuum pressure?

If the above show up as fine then use a bottle of Redline S1 with a half a tank of fuel then change the oil after a week.

If that fails check the compression on that cylinder.

[96qtrip]

END of topic!!! FIXED IT! Thanks to those who offered ideas. Problems inthe final answer were:

bad coil pack on #7, loose pin in the 8 pin injector connector on # 3 cyl. ALL better
and it pulls hard once again! Go baby!!!

[kevindanielk]

Do you mind detailing how you diagnosed the problem as a bad #7 coil and a loose #3 injector harness wire pin? Curiosity, just curosity, since my 95 also stumbles a bit at idle once warmed up.

[96qtrip]

Pretty much as listed in the post - A code reader is a must. The intermittent symptoms suggested plugs, but the order of diagnosis was "item checked" (what and where to check for)

fuel system flow and pressure ( filter and pump)
vacuum leaks, hoses, EGR and IACC plumbing and clean MAF - (always check points on this engine had a Borg hose in my ear)
injectors (stethoscope and connector readings at head connector)
ignition and plugs ( ecm output, camshaft sensor) and plug tips -they were three years old)

after replacing the defective hoses, adding new plugs WYAIT - the suspected coil pack was moved
from cylinder 7 to cylinder 5 - and the code went with it. The # 3 connector pin on the eight pin harness adjustment cleared that injector problem as well.

Hope this helps

[Haitian_King]

@96qtrip

How did you fix the loose pin?

[kevindanielk]

Thanks for your fix explanation, 96qtrip.

[kevindanielk]

Just a follow-up to my rough idle problem;

Fixed my rough idle by changing a short piece of hose located just to the right, under the throttle body and behind the egr valve, which I had to remove. That 5" long hose had a sizeable hole in the elbow, where it turned to go under the intake. After changing all the plugs still didn't help the idle, I just started to think simple; I noticed that my engine was sounding a little Iouder, for a few weeks. Suffice to say, only then did I notice the loud vacuum leak coming from the 1/2" hole in that hose. Stupid deteriorated rubber! I now wish I had just paid a little more attention to my engine before changing all my plugs, since they looked just as good as the new ones I put in(after four years). But, problem is fixed and my Q is once again idling as smooth as churned butter.