Today I replaced the completely worn out shocks on my 1990 D-150 (5.2 2WD) and all went well other than a busted knuckle but I couldnt find the exact problem I want to tackle next in the search forum so here it goes:

I have excessive carbon puking out of the tail pipe (no smoke) and when I start from cold it fires right up but idles rough for a few minutes and kind of stumbles if I try to take off right away. Starts right up and purrs like a kitten when its warm and it has plenty of power and runs smooth after the first few minutes.

My thoughts are that its obviously running rich (but its not throwing any adverse codes and the CEL isnt on) as the plugs were carbon coated when I replaced them today. I plan on replacing the CAT and 02 sensor but is there anything else I should be looking at? I would think if the MAF was bad it would be causing me problems during driving and not just at start-up.

 

I have a 1989 ram w150 with the 318, and I have the problem with rough idle as well but, my idles rough all the time and overfuels badly at idle, down the road isn't bad, just it seams it's got more power sometimes then others, my problem is my MAP sensor ( there is no MAF sensor), so I unplugged the sensor and started it ( a lot times I've heard if it starts the sensor is out), and it ran PERFECT no miss, no rough idle, just smooth, and to make sure it was that sensor I plugged and unplugged the sensor a few times while it was running, when I plugged it in while running it went from perfect to just awfull again, and when I plugged it in after 1 or 2 seconds it almost die, then rpms go back up a little, once you unplug the sensor if its out, the computer will go to a predetermined fuel mixture and that's why it will run better, mine also idles a little too slow and that was also better when I unplugged the MAP sensor, it's something I would suggest you try, i cant guarantee it the source of your problem, but its worth a shot, mine also doesn't throw any codes or turn on the check engine light either, hope this helps.

 

You vehicle relies on the coolant temp sensor (pretend it is the choke on a carb'ed engine). If it isn't working correctly the computer doesn't know how much fuel to pump in and is especially bad when cold.

Test your CTS.

 

Thanks for the replies; yea I meant MAP sensor...I'm getting confused with all the different acronyms! I will give unplugging it a shot thanks...it would be great if it is such a simple fix. I will also have to test the CTS, I assume I'll have to drain some of the antifreeze to replace it which might just be a good preventative option and give me the incentive to flush the radiator anyway.

I originally was looking for just a parts truck for my 86 Ram project but this 90 is in such good shape and it runs so well that I now have two project RAMs, I just wish parts were more available and not so expensive. I am missing one small round center cap from one of the 8 hole factory mags that are all in excellent shape and the only one I could find on line was $90.00!

 

Do you have a Factory Service Manual?

If not here are the specs for the CTS:
7k - 13k Ohms @ 70 degrees
700 - 1k Ohms @ 200 degrees

If you want to test the TB Temp Sensor while your at it:
5,600 - 14,600 Ohms @ 70 degrees
400 - 1,500 Ohms @ 200 degrees

If the CTS tests bad you don't really need to drain the coolant, just take out the old one and quickly install the new one and you will only loose a small amount of coolant
IMPORTANT: do this with the engine cold so here is no pressure on the system.

 

I have a Chiltons but it doesnt really give much information on cause and effect; i.e., trouble shooting, so I appreciate the pointers.