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I originally thought it was an intake problem, Now I think this is electrical. I attacked everything intake already, EGR, IAC, TPS, Map sensor, O2 sensors, multiple relays, Fuel pump & filter, plugs and wires, dis.cap, cleaned the fuel injectors, I ran a redundant ground, air filter. The thing is, the speedometer Jumps and/or Reads 0mph or 120mph while it idles rough and/or high wanting to stall or not. If it stalls, it starts right back up. If it doesn't stall It'll just idle crazy and I have no power when I step on the gas, if I keep driving it'll jump and hesitate sometimes. It feels like a transmission slipping sometimes and it can get stuck in overdrive and doesn't want to shift, It even backfires sometimes too. It definitely burns rich when it screws up. Eventually it will stop messing up and drive perfect after a few minutes and the speedometer works too. I think it might be the ECM but what else could it be? Instrument cluster? It has to be electrical. It starts fine every time, runs good for 5 or 10 minutes, then as soon as the speedometer goes crazy the car goes crazy... It idles high or low, jumps and hesitates with no power mostly, then runs fine again after messing up for a while, depending on the trip It might do it once or twice at random intervals. I put $800 in this thing and still haven't fixed it, someone help please.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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Since you did a redundant ground you must have already checked the battery connections several times. That's all I can think of is battery connection issues or maybe the ECM. The ECM wouldn't make the instrument panel go crazy though (I don't think). Maybe it will if it's a digital IP. That rich running sounds a lot like a MAP sensor problem, but that wouldn't affect the IP. weird.
 
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