This car is driving me nuts.......First of all the car has an occasional engine miss. Sometimes is worse than others, when it is bad it is pretty bad. I put my scanner on it and I got engine misfires cylinder 1, 2, and 3 and random misfire. I also had a IAT sensor code.....not sure what that is. Ok here is the kicker. I changed all plugs and only the wires on the cylinders that had the misfire codes trying to save alittle cash. I did this and went and drove the car, the car does fine until I really give it alot of throttle, then it really bogs down and the check engine light comes back on and it runs bad again. I put the tester on the car and it still has the same codes it had before I replaced the plugs and wires, but now also has cylinder 5 misfire. I erased the codes and tried it again. Car did fine until I put it under a heavy load, same thing happened bogged down running awful and CEL appeared. Put the tester back on it, had all the same codes cylinder 1,2,3,5 and multi misfire and IAT. I now changed the coils on the original three bad cylinders 1-2-3 went and drove the car and the same thing happened again but now I got all the same misfires 1-2-3-5 and multi but now I got cylinder 8 added. I don't know what is going on with this car could something else be causing this? I would understand if I got different codes each time I suppose but not for cylinders 1,2 or 3. I have changed the plugs, wires and coils on all three of those cylinders and still get a misfire code for each one. I am at the end of my knowledge with this problem all help is appreciated.

Which IAT code did you get?
P0109
P0111
P0112
P0113
P0114

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

You can try taking out the upstream o2 sensors (the ones right after the front cat), leave them out and go take it for a quick spin with crazy loud exhaust(set the o2 sensors aside in a safe place). See if it makes the condition any better or not, the cats could very well be clogged up. Another possible option could be an air mass.

Yes, the coils are not your problem since it affects multiple cylinders. IAT is inlet air temperature, so this is pointing towards the MAF sensor.

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Prost!

First I would check fuel pressure & delivery...then
I would have the exhaust back-pressure tested & IF it is OK then the Mass air flow sensor is a good possibility.

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If you are testing for an obstructed cat it seems like you would want to remove the O2 sensors that were located before the converter, not the ones that are located after the converter.

I agree with this diagnosis, but a better test is to use a threaded adapter that screws into the front O2 mount to check the exhaust system back pressure before the front cats. At idle you should only see 1-2 PSI and at full-throttle the pressure shouldn't rise to more than 5-6 PSI.

I also agree with the other posts about an air-mass meter being a probable cause, adaptations should be checked to rule that one out before looking at the converters.

If the cat is plugged you'll see back pressure in the hundred PSI range before the engine starts to bog down, the test is pretty easy and its definitive.

I recently replaced the converters in a CLK430 and I was unimpressed with the quality of the OEM converters. The assembly is beautifully done in stainless steel but the converter matrix assembly is held internally in place with a couple of pinch points that are created by an external crimp to the converter case. If one or two of these pinch-points fail, or the converter fractures slightly the entire assembly will rattle around inside the converter. A good test is to jack-up the car and lightly tap the converter assemblies, if you can hear rattles that's not a good sign.

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98 Dodge-Cummins pickup (123k)
13 GLK250 (135k)
06 E320CDI (323K)
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Thanks alot everyone, it was indeed the right side cat. converter causing the whole issue. Problem is now solved. Thanks

Yea, i meant the first o2 ( i did say upstream, then contradicted myslef....it was late....and after the ruination)