: Hitting rev limiter in idle after startup

Mark C
02-15-09, 06:38 PM
I washed the top of my Seviiles engine yesterday to clean some oil off the front valve cover and apparently I got something wet that shouldn't be wet. Car started and ran fine yesterday after washing it, although I didn't drive it anywhere. My wife took it this morning and got about a mile away and it started running really rough and then it died. Wouldn't restart so had it towed home. Had some water down in the front plug wells, blew that out and cleaned the plugs both on the outside and electrode ends. Had a couple of codes P0371 IC24X reference CKT too many pulses, P0340 IC Module cam reference CKT no frequency, P1375 IC 24X Reference Circuit High Voltage, plus P1599 Stall or near stall detected. Cranked the car for quite a while after putting the plugs back in and got it running, but it backfired a few times and gave me a MAF code Mass Air Flow (MAF) Sensor Circuit Low Frequency , and Map code P1108 - BARO to MAP Sensor Comparison Too High. It was barely running almost like it was running on 5 or 6 cylinders, and would stall frequently. I went around and cleaned out all the electrical connectors I could get to with electrical contact cleaner, none were visibly wet or even moist that I could see. I ran through the diagnostics for a bad cam sensor and crank sensors and they check out OK. The car starts right up now, but as soon as it starts its runs right up to the 4200 RPM rev limiter without touching the gas pedal. Current codes are P0101 - Mass Air Flow (MAF) Sensor Performance , P0121 - TP Sensor Circuit Insufficient Activity , and P0371 - IC 24X Reference Circuit Too Many Pulses.

Theres no mechanical binding of the throttle and the throttle is closed while this is happening. I think the overpressure door on the intake is closed after the backfires, but I can't actually see it. I assume I'm looking at a new ICM, which I have, but is there anything else that can cause the engine to run at full throttle on start.

02-15-09, 06:47 PM
Just a guess, but MAF (Mass Air), TPS (Throttle Position) or IAC (Idle Air) may be sending a false signal. Wet connectors ??

Is there any water down in the valley under the intake manifold ?? If so, it needs to be vacuumed/blown out. Your starter motor is next on the OOC list.

02-15-09, 08:05 PM
It has to be getting excess air from somewhere to feed it to get the RPMs to get it to the REV limiter. My guess is the overpressure door.

Mark C
02-15-09, 10:34 PM
I have no doubt there is water in some connector somewhere, just havent found it yet. I havent disconnected the throttle position sensor yet, but thats the only one I haven't out of the list thats associated with the DTCs. If theres water down in the vally there shouldn't be alot, I didn't flood the top of the engine with water, just enough to hose of the cleaner from the front valve cover area. I'll check that out tomorrow morning but I don't think it should be an issue.

Even if there was a hole in the intake why would the rpms run away like its doing. Where is the PCM getting the signal to fire the injectors? Doesn't the PCM look at the cam and crankshaft sensors, the MAF signal, throttle position and MAP sensor info (in the case of the 97's) to determine the dwell time and frequency of firing the injectors to cause the RPMs to increase? I would think that throttle position must be the major controlling input in this case. But what does "Insuffcient Activity" mean?

If the door was partially open it wouldn't it just act like a vacuum leak and idle really poorly?

02-15-09, 10:56 PM
No. If the door was stuck partially open it will act just like an open throttle plate. Remember that an engine wants to run WOT. It has to be choked down to control it. That's what the throttle plate does. When you step on the gas, you're not "giving it gas". You are opening the throttle plate and unrestricting it's breathing, allowing it to breath more like the way it wants to (wide open). Remove the TB and start the engine. It will run WOT (unrestricted). Like wise on the '93/'93 Northstars, if you remove the top of the manifold (big hole in the manifold now) and start the car. It will run away unthrottled, wide open.

Is this the '97 or the 2000 you're talking about?

Mark C
02-16-09, 12:43 AM
Its the 97. Looks like I'll be pulling the intake tomorrow.

What does the 24X too many pulses from the ICM do to the PCM. Is it essentially just indicating that there is noise on the circuit between the ICM and PCM?

Mark C
02-16-09, 04:48 PM
Well not only was the overpressure door open, it was blown completely out of the manifold and leaning up against the back of the power steering pump. Nothing was broken on it so I just clipped it right back into the car. Then I got a P0300 random misfire code, but it was really just cylinder 6 that had no spark, kind of weird because cylinder 5 (the opposite one on the same coil) did have a spark. So I swapped in a spare ICM and I'm back in business. No current codes at the moment. Now I'm off to Rhode Island to see if everything is back to normal.

02-16-09, 05:09 PM
Must have been one hell of a backfire. Glad you got it fixed.