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Discussion Starter #1
Hi Folks,

So Chancho has been running top-notch for the past few weeks and I couldn't be happier! I took him on his first real back country adventure since I did a ton of work to him and he crushed it. This was a relief, considering I'm a beginner mechanic and have very little faith in my work!

Here's Chancho crossing a creek about 3 hours into the 4 hour drive.



Anyhow, I drove him to dinner tonight and on the way home, I noticed a very slight flucuation in RPMs at about 20mph (2nd gear, I think). I had my foot steady but the RPMS would go up and down maybe 200 or so RPM's (very slightly). It was audible but not big enough to surge or buck or what have you.

Anyhow, what do you think? I've already cleaned at out the IAC, so I'm guessing TPS? Maybe a vacuum tube? Anything else to consider?

EDIT FOR FUTURE SEARCHES:

Other symptoms that I wasn't aware of included very poor low end accelleration, very strange idle flucuation immediately after ignition that tapered out to normal idle after about 1.5 minutes. Also uneven engine response depending on throttle position. I probably had very poor MPG, too, and I'll comment on that if it does improve.

THANKS
 

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Kitteh Commandaar!
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That's nothing...wait untill the motor revs all by itself from 1.5k to 5.5k rpms all by itself.........it's....interesting to say the least :toothless

Dunno. If it's not missing, it's hard to say :scratchhe Check vac lins and possibly fuel pressure....could just be the tach is getting old :shrug

KC
 

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Discussion Starter #4
I'll check all the vacuum lines again. Engine IS reving, not just a tach issue. :banghead
 

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Discussion Starter #7
Cap, rotor, plugs, wires, coil... And make sure the wires are routed EXACTLY right.

These have all been replaced recently but...what do you mean by routing them "exactly right?" Does it matter as long as the firing order is correct?
 

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Discussion Starter #9
Sorry, Steve. I couldn't see it at work. Thanks....I didn't realize that mattered and will reroute accordingly.
 

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Discussion Starter #11
Update: I rerouted the wires according to Steve's diagram (thanks, Steve). Unfortunately, it's not any better so I pulled codes and got a 22, which I believe to be a MAP sensor problem. Correct me if I'm wrong, but I'm thinking this further supports my vaccuum line theory. Anyone know of any specific lines I should check first? Other suggestions?
 

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Check the tube on the back of the heads. Use starter fluid or carb cleaner and spray the lines, if rpms increase, you have found the leak/leaks.
 

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Kitteh Commandaar!
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Also, you could test the MAP sensor using the Haynes proceedure...or...you could take it to the zone. They'll test it for nothin', beware though...you should probably have more than 1 set of hands to test it. :rofl:

KC
 

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Discussion Starter #16
Are you absolutely certain you didn't get code 11? All the codes are flashed-out twice. ;)

http://fullsizebronco.com/forum/showthread.php?t=44736

To practise reading codes on an '85-95, warm up the engine, then unplug the MAP/MAF & the fuel pump relay. Then pull codes & make sure you're coming up with the right numbers since you'll know what codes to expect.
It was a 22 (I did it three times) but now you've got me all nervous so maybe I'll do it a fourth!

Seems like a MAP error would make sense for the symptoms, don't you think?

OT: I replaced the PCV valve today--the old one was soooo covered in soot, it took me a second to find it because it looked like a mound! The previous owner musta been a real POS.
 

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Discussion Starter #18
No vacuum leaks that I can find--took a can of carb cleaner to it and found nothing. Also, it idles like a champ.

I think I've realized that the fluctuation occurs at a given throttle position (i.e. foot down a just a bit) than at a particular RPM range. TPS, huh?
 

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Discussion Starter #20
Yeah, I'm not too too good with electrical gadgets and the like. I really don't know very much about it, other than the concept of a circuit and how relays work, so I'll probably just end up replacing the thing or posting a bunch of results that make no sense to those of you who do understand that stuff.

Auto parts stores are closed on Sundays here...suck. So I'll take this up on Monday with either a new voltmeter or a new TPS, depending on what I can afford. Thanks for your help, as always, Steve. :beer
 
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