Couple problems with my truck

[bigern26]

I know I am not in the Mazda section but this is not really mazda specific I think.
I have a 1994 Mazda B4000 4x4 with a 4.0 and 5 speed.
I am having a couple problems that I am hoping you all can help me out with

When the truck is warmed up and I am accelerating it sounds like a diesel.
There is like a knocking sound and it gets worse when I am going up a hill or under load. as soon as I plane out or let off it stops. It is really annoying and it does seem like a power loss. it almost sounds like it is out of time but its electronic ignition. It does not miss and does not do it when its cold.

I have just replaced plugs and wires and that did not help.

The other problem is high idle, It just started this the other day. when I start it up it will idle to about 2000 then slowly drop down to about 1300. Could this be the IAC?

Thanks in advance for any help.

 

[adsm08]

So it knocks. That is commonly a carbon build-up issue. The carbon deposit causes a hot spot in the cylinder and lights the fuel too soon.

The cheap thing to try first is seafoam. It will break up and wash out and carbon that might be in there.

The idle issue could be an IAC. Hit the IAC with some carb cleaner or gum cutter. I really like this stuff called 2+2 if you can find it.

 

[PanamaExpat]

Another thing you can do is an Italian tune up. Find a nice long stretch of open road put it in 4th gear and floor it. She will top out before you red line and just keep pushing it. You will know you were successful when she blows a large puff of black yuck out the tail pipe. I'll probably get some razzing for this suggestion but it does work. I have to do this to my diesel about every 4 to 6 months because of all the around town chugging it does. She runs so much smoother afterwards.

http://en.wikipedia.org/wiki/Italian_tuneup

 

[bigern26]

I will try the seafoam and see what that does.

Thanks

 

[Jim Oaks]

Another thing you can do is an Italian tune up. Find a nice long stretch of open road put it in 4th gear and floor it. She will top out before you red line and just keep pushing it. You will know you were successful when she blows a large puff of black yuck out the tail pipe. I'll probably get some razzing for this suggestion but it does work. I have to do this to my diesel about every 4 to 6 months because of all the around town chugging it does. She runs so much smoother afterwards.

http://en.wikipedia.org/wiki/Italian_tuneup

I actually worked with a guy that had a fullsize Blazer that wasn't running that great. He took it to a mechanic, and the mechanic took it out on the interstate, floored it, and blew it out. Ran much better after that.

 

[bigern26]

Well I got the idle under control, I found a small vacuum line that was disconnected.

I tried the seafoam and it did not help any.

 

[97ranger xlt]

italian tuneup ..

 

[bigern26]

italian tuneup ..

I will try that as soon as I can find a road that I can top it out in 4th gear. That will have me speeding at a high rate as I am at 65 mph and not even hitting 2000prm yet in 4th.

 

[johnday]

I will try that as soon as I can find a road that I can top it out in 4th gear. That will have me speeding at a high rate as I am at 65 mph and not even hitting 2000prm yet in 4th.

Speed limits are nothing but a suggestion anymore. Try 3rd gear and bring the rpm's up then.