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Still death-traps on the road

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dnix71:
JW I have scan tool, but there are no codes set. Ford didn't set logic traps for enough possible aberrant conditions. Even the codes set many times don't tell you what is really going on. My neighbor has a 2006 Hyundia Sonata. The rubber tube that connects the air intake to the manifold had cracks that were not visible from above. The computer set 4 codes, mostly about #4 cylinder misfire and a possible bad coil pack. He had surge at idle and sometimes the engine would just quit. A google search revealed all 4 codes could be a vacuum leak, so I removed the part and showed him the crack, plus a rotted 4 inch vacuum line.

The cracked tube cost $200, so I wrapped it in electrical tape and that fixed it immediately, without even having to rest the ECM.

My own Toyota acts wonky when the exhaust gasket goes bad. This has happened twice. After the Challenger disaster you would think people would just know that 0-rings and hot exhaust gasses are a bad mix, but Nooo, not Toyota.
The O2 sensor is 4 inches below the leaky fitting and sees air leaking in and begins to run rough. The o-ring needs to stay compressed to maintain a seal, but asbestos is illegal now, so they use silica, which cracks and falls out. I have resorted to adding a wire inside where the silica fell out. That sort of fixes it.

JW:
Are you using after market gaskets, Toyota typically uses metal gaskets. I wouldn't worry to much about the bad O2 sensor readings, the ECM will just go into open loop and the engine will run just fine, but with worse gas mileage.

dnix71:
That's what happens. My gas mileage goes down and the engine runs rich. The aftermarket gaskets I use are metal, but the design requires compression, which metal doesn't do. The two cast iron flanges are machined flat and in the middle is a ring of material removed for the gasket. Twice now I have had nuts fall off one side as well. One side has a stud threaded through and tanged so it won't come out. That stud prevents the Cat pipe from dropping off onto the road. The other side is a bolt. I don't know why they didn't just make the surface flat and use a plain metal exhaust gasket like the one between the block and header. I don't see why I couldn't add one if I found one the correct diameter, except that maybe the exhaust header needs to transfer heat to the cat pipe by direct contact. I have heard of the headers cracking, but so far mine hasn't.

The gas mileage matters. I do 35 miles a day in stop and go city traffic just to get to and from work. I had a Ford van before the move and I would be in financial trouble if I still had the van. It only got 15 MPG around town. The Toyota gets over 40 MPG on the highway and about 30 MPG in town. Plus even though it is 20 years old, everything still works and it turns easily. Doing a u-turn in the Ford usually meant a 3-point turn, and stopping traffic, or going wide right to shave a lane.

Warpspeed:
There is usually an idle speed air control valve that admits air around the throttle.
That could also cause sudden changes in engine speed.

JW is right, the drive by wire system itself is a dual redundant system that is designed to be fail safe for very obvious reasons.
But there are other ways besides the actual throttle that can admit air into the engine, including faulty split rubber vacuum hoses, leaking gaskets, and electrical problems with the fast idle system.

joestue:
The computer in my s-10 would randomly decide that the engine should idle at 2K-2.4K rpm via the idle air control valve.

Usually this isn't a serious problem on most cars because there isn't enough air available to make it a driving hazard. In my case, the engine runs find with the idle air control valve disconnected, so I disconnected the cable when it was idling at 700rpm. might be safe to say most cars will not run without the idle air control valve because the ecu was not programed by engineers who care about reliability. some cars have a pressure sensor on the power steering pump, the ecu will increase idle speed if the pressure falls. only problem being there is no upper limit. i have heard of cars revving to 3000+ rpm if that sensor fails or if the wire breaks.

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