I had a very simular issue have you check your MAF Sensor unplug it when if it runs fine that's your issue look up the MAF (Mass Airflow Sensor).hi, I have a 93 ford explorer. that I just put a new motor in. before I started the new motor I put an aftermarket air assembly on it. when I started it, it gets a high idle about 2000 rpms, then drops down and pulsates. so I put the original air box back in, and got the same thing. when I start driving, all is well runs perfect idles perfect. when I stop and let it set for a few minutes, it starts right up, and pulsates and has a small shake to it. again as soon as I start to move it, all is well. only has problem on startup. ok. what I have done to it. new 4.0 motor, new heads, new fuel injectors, all new gaskets on engine and intake, new iat sensor,new iat sensor,new maf sensor with new body, new tps sensor, cleaned throttle body,new air tube from air box to throttle body, computer from junk yard,sprayed either around cold running motor to find any vac leaks found none.no check engine light, no codes. when I start it cold, and immediately put it in gear, I get a high but steady idle, no pulsating. anyone got any ideas please let me know, I,m kind of stuck right now. were I didn't have this problem before the new motor, I assume I did something wrong, but what I don't know. but once I put it in gear and go, it runs and idles perfect. thank's for reading all this. bob. p/s it's a limited 4 wheel drive.
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