Symptoms:
(1) Car is hard to start, takes 3 or 4 cranks to get it to stumble into a start.
(2) Engine won't rev past 1800rpm exactly, seems exactly like a fuel cut limiter.
(3) Engine rev's up and down between around 1200 and 1800, I think it wants to rev higher, but the 1800 limit kicks it back down.
(4) If I put the car in drive with my foot on the brake and just sit there, it will hold rpm at 1100, and slowly start to drop until it dies.
(5) I have a short ram intake. You can always hear it breathe, but now it's extra loud. Sounds like a big bad alien breathing.
(6) Radiator fans run constantly at full speed as long as the engines on, whether it's cold or warmed up.

Story: A little over a month ago I swapped in a DE-K, everything ran PERFECT except that I had an exhaust leak. I used a really cheap ebay header/y-pipe setup, and ended up cracking one of the welds on the left bank header. I bought the OBX headers to swap on. Two saturdays ago I started to change the headers. I got as far as taking off the upper intake mani/plenum before I realized that I didn't have plugs for the extra pair of o2 bungs. So I put everything back together. At first the car wouldn't stay running, so i loosened the plenum and retightened it fearing that my friend who was helping me didn't use the correct bolt sequence. I also noticed the IACV (I'm using the 5th gen with modified 4th gen connector) wasn't fully tightened down, so I cranked it down, and the car started up and idled fine, but it would die everything I came to a stop. I parked it, and a week later changed the headers. Only thing I removed was the upper plenum and cross member, and replaced the right bank (rear) o2 sensor. First time I started the car I forgot to hook up the crank case ventilation between the left and right valve cover's. Hooked that up, started fine, but started showing symptoms. It would still rev all the way up past 1800 though, and the fan's weren't going constantly. I drove it home, let it sit for a day, and the next day after trying to get it running right the 1800 limit and constant fans started.

What I've Done: I checked for external vacuum leaks using B12/carb cleaner, no leaks that I can find. I rechecked all vacuum lines and sensor connectors. I disconnected the battery and let it sit over night thinking maybe it was in fail safe mode, and that this would reset it. Next day I started it up and still had all of the same problems. I borrowed a OBD-II code reader from a friend, but now it's not throwing any codes. I'm completely baffled here.

I'm thinking it might be something with the IACV, or possibly the MAF. But i just don't understand the 1800rpm limit and the fans running constantly. Has anybody experienced any of this? Tomorrow I'm going to pull out the IACV and clean it all out and check the MAF with a multimeter. Any other ideas? Maybe the coolant temp sensor? If that was going bad, would my temp gauge still work in my cluster? My minds warped from this one. Thanks in advance for any help.

 

Check the maf, fix the exhaust leaks and report back.

 

exhaust leaks were fixed when I changed my headers/y-pipe. I'll check the maf and try to clean out the iacv the best I can without removing the entire housing.

 

^^ that still don't explain the constant fan. My bet is maf on the other subject. If you do find out that it is it, i have an extra one for sale if you need it. I hope that isn't it tho. Best fix's are money free ones

 

werd, i'll let you know if I need it.

 

Ok, yesterday I took the TB/IACV off and cleaned it all out. Started the car and it still had a hard time getting going, but would pretty much start right up after that. It would die if I didn't keep some gas on it. I checked the MAF, it's sending the right signal. Then we checked the coolant sensor, and sure enough it seems to be telling the ecm that it's running WAY too hot. 250 ohms is 194' F. At operating temp we got a reading of 54 ohms, the lower the resistance the hotter temperature it's reading. That would explain why the fans are constantly on, and maybe why the ecm's cutting fuel at 1800rpm. Maybe it's some sort of fail safe in the event of an overheating engine. After work I'm getting a 250ohm resistor and put it in between the terminals, if it runs fine after that, I know what I have to do.

Has anyone come across anything like this before?

 

Coolant temp sensor. Replaced it and now she runs like a peach.

 

CTS or MAP was my guess. Good call!

 

Amazing how the CTS failure effects the computer. Good job on figuring out that one

 

Thanks guys. It was in the back of my mind the whole time, but I thought it had to be something that I touched during the header/y install. Just too much of a coincidence in the timing. I pull in intake to do the install and all of a sudden my car wont run. What are the odds. The constant running fans tipped me off. I'm glad it was something simple.