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$100 Reward for Correct Diagnosis

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sonicss31

Well-known member
:banghead:I'm out of ideas, so lets have some fun and maybe put a little cash in your pocket. 1997 454 Mag MPI runs great at all speeds but will not idle and seems to be running rich at low speeds (less than 1500 rpm). Here is what I have tried so far;
spark plugs and wires, ignition module, IAC controller, thermostat (160), temp sender, temp switch, checked grounds, checked battery switch, compression test (140 to 150) all cylinders, no leak down done, TPS and MAP sensors, fuel injectors cleaned (not professionally), no vacuum leaks detected, fuel filter/seperator, VST tank screens and pump, diaphram in top of VST tank, fuel pressure regulator. That is all I can remember for now. I like a challenge but this is wearing me down. I will post this on the other 2 sites for those that have a preference. The winner will be publicly acknowledged unless otherwise directed. I have searched many forums for this problem as you can see by the things checked already. Help before there is a large pile of melted fiberglass in my yard.
 
Have you hooked a scan tool up.

Sounds like IAC ( I know you replaced it ) or related wiring.

Or a ECU issue, hook the scan tool up and see if it connects at all.
 
You need to lock the timing up on the dianostic plug and check the base timing it should be 8 degree's. Then make sure your TPS reads .500 with key on and the throttle shut. If you have a scan tool make sure the throttle reads under 1 % when the throttle is shut or the ecu will not go into a closed loop and control your Iac and spark stabilizer.
 
take the little screen out of the fuel cooler just under the regulator.. leave it out...

i'll PM you my address for the $$$ LOL
 
You replaced IAC valve, BUT, did you clean the air passage behind it. If the air passage is plugged up, no air will get in at idle. Hence the not idling, but runs great off idle. Its like air bleeds for carbs. Clogged idle air bleeds=rich idle/stalling
 
Thanks for all the replies so far. Will start the elimination process again Fri. Have a schedule set up for scan tool and tech. early next week. Keep um coming:)
 
X3 on the IAC. Just had to replace mine for same symptons but I did have the alarm sounding and helped a lot from obnoxus having the scan tool. When it failed, it went in guardian mode and wiped out all the spark plugs because it ran super rich. I did have to change plugs after changing the IAC. Also check the throttle body port and make sure it is not dirty. I am assuming you did check cap and rotor for corrosion and spray ignition wires with water to make sure they are not arching.
 
If you can't get it straight i will be glad to look at it for you,located in edgewater,md 30-40 minutes from you,I have a ASNU fuel injector cleaner and flow tester and have found a lot of strange problems with the 454/502 efi injectors most of them were made by weber,give me a call if you need some help Dave 410-956-5381
 
How did you clean the injectors? Did you do a flow test? If you only externaly cleaned them you would not know if an injector has stuck open. What were the plugs like did they look the same(tip colour)?
 
Check number 8 spark plug to see if it's excessively rich.

Also you need to do a injector balance test.

Also You will want to check the fuel pressure at the mechanical fuel pump as well, If it's over 8 psi then you will need to replace it.
 
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Not forgotten, did check fuel pressure today seems good at 40psi with no leakdown, timing ok, IAC working fine. Still a day or so away from scan tool check. I'm leaning towards something temp related because it runs fine on the hose, put it in the water for a test and did the same sh*t. Might not be seeing the temp sensor
 
I believe the IAC valve itself can be functioning, but if the port that lets the air into the engine is plugged, it wont get air at idle, and stall. Like in the old days of putting your hands over the carb and choking it out.

If you open the throttle a touch, does it stay running and smooth say at like 1200rpm? Or is it sluggish and feel like its misfiring?
 
thats a simple one the injectors are leaking/barrel valve is flooding the cyclinders
i dont know what you got but we use to hook the leak down tester up to our hilborn and set it all that way i cant remember the exsact number but i think its like 15 to 18 % for 1100/1500 idel
 
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