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Old 02-05-2010, 10:28 AM
Scott Scott is offline
Liking the Ford Ranger Forum
 
Join Date: Jan 2010
Posts: 24
Default HELP! Rough idle/high rpms when stopping

Ok here's my situation: 97 2wd 2.3 Lima 5 speed, 150,000 miles. Blew a head gasket about 6 months ago. Tore her down, find out the head is cracked between the valves in cylinders 2 and 3. Buy new head and install as per specs. Also installed at this time: new plugs, wires, coils, water pump, thermostat, fuel filter, all short block gaskets,timing belt and serpentine belt. First turn of the key she fires up hallelujah. She runs good for about 4 months, then I start to run into rough idle. Started very faint but has gotten to the point that I have to brake and gas while stopped. Also the motor will rev pretty high (don't have a tach, but feels like 4-5k) when I let in the clutch to coast to a stop, so I have to keep it in gear to engine brake. After checking my handy dandy Haynes, decided I had an intake problem, and so far have replace the IAC and TPS, disassembled and cleaned the throttle body, and the same for the MAF. She's still having idle issues and high rpm coming out of gear, although after cleaning all this crap the throttle response is great.

Before you ask, I'm positive the timing is correct, double triple checked. One thing I'm not sure of is the exhaust. I'm running the OG O2 sensors, and my exhaust has a rattle at about 2 grand in every gear (I think its coming from the cat). I have a new upstream O2 sensor, I just can't unplug the old one to swap it in (any tips?). I can get to the connection, but it's in a very awkward spot and I haven't been able to disconnect. I did remove the upstream sensor from the exhaust pipe thinking it may allow the exhaust to escape better if the cat was clogged but the idle issue was still there.

The CEL shows insufficient egr pressure. I can't find any vac leaks, so I think the egr tube may be fouled up at the valve/gate where it comes off of the exhaust manifold. I don't think this would cause my idle issue though. One other thing to note, the idle issue usually doesn't appear immediately at start-up, she will run fine for a minute or two and then swan dive.

When in gear and under a load, the engine runs great, better than it has in years actually. Would a faulty O2 sensor cause this? Or does it sound more like a clogged cat? If the cat was clogged I'd think that unplugging the upstream O2 sensor would help diagnose that, but it runs the same.

I'm about to buy a new cat, probably the rest of the exhaust while I'm at it, but I just need to talk to someone about this. It's a lonely road trying to reverse engineer my beloved ranger, although I will say this and other forums have been absolutely extremely helpful. This thing is giving me gray hair, and I'm only 27. Any ideas O wise ones? Help a brother out!
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1997 Ford Ranger XLT short bed regular cab
2.3L Lima
5 speed manual
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