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I have a 88 t bird with the 5.0 and an AOD. I bought it sight unseen (lesson learned) I was told by the seller that the car only needed an EGR valve to run right. I did a little exploration, and blocked the EGR off. Not change in the idle. I`ve replaced the fuel filter, TPS, IAC, and tried different MAP sensors. I also installed an MSD coil and splitfire plug wires to tune it up a bit. Basically when you first start it the car "hunts" for an idle speed, idling down to the point it almost and sometimes does die, then if it doesn`t die the idle reves up to a more normal speed, and then repeats this process till the engine seems to hit a decent operating temp and the idle smooths out. Problem is too, that once the idle smooths out as the engine warms up, the throttle still has a "stumble" or a hesitation, sometimes popping like a backfire in the intake. I`ve tried to drive it once the idle smooths out but it bogs terribly. I have no way to check codes, so is there anyone who might have an idea what I should look for or change?

Thanks to all for help!
 

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Maybe a vaccuum leak? Maybe while it's running at idle, spray some carb cleaner around all the vac. fittings and whatnot and see if it changes the idle any. My dad's 5.0 had this issue and it turned out that the upper plenum gasket was leaking.

Jay
 

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Is the EGR system working right? On my '91 5.0, at least, the EGR valve sends a voltage signal to the ECU, the voltage increasing as the valve opens more. The ECU then sends a current out to a electric/vacuum switch. This changes the vacuum signal going to the EGR valve, opening it more or less depending on coolant temp, load, etc.

But here's the thing--there's almost no fuel or air in the exhaust gas. So when the EGR opens and lets it into the intake manifold, it takes up some of the volume that otherwise would be intake air. So, the ECU cuts back the fuel to the injectors to keep the fuel-air ratio constant. When the EGR is wide open, the fuel is reduced by 2-3%.

All that happens, whether the EGR passage is blocked off or not. So if it is, the ECU is cutting back the fuel slightly, but the intake manifold contains 100% air. The result will be to make the engine run lean--maybe more than the O2 sensors can compensate for. This would make the car hestitate, bog, etc. when it's warmed up. You might want to change the O2 sensor(s) also.
 
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