rough idle

[imdawrlus]

for the past couple weeks or so, in the morning when i go to start my truck, it idles EXTREEMLLY rough for probablly 10 seconds or so and then idles fine....also my mileage has been down recentlly and i'm thinking that it has something to do with it.....fuel filter replaced last fall anlong with spark plugs and advanced timing......last winter i put in plug wires, cap and rotor.....can anyone else think of things to check?? i'm leaning twords the iac.....thanks!!

[biglouie_underpressure]

how does your pcv look?

[imdawrlus]

i changed that last winter.....someone elso also mentioned the coolant tempature sensor...i'm going to give that a try....

[biglouie_underpressure]

Running rich?

[bvr775]

i'm leaning twords the iac.....thanks!!


have you checked it yet

[imdawrlus]

nah i havent checked it yet...i havent hade time....and plus that shouldent effect my mileage as much as a temp sensor.......i allready bought one for 9 bucks at autozone....where is it on the 4.3?? i heard its on the head in between two of the spark plugs but i dont know which ones or what side....anyone know?? also, can the coolant temp sensor cause it to run rough ONLY for a few seconds on the FIRST startup of the day??? THANKS!!

[Matt 4.3 TBI]

There are 2 temp sensors. The one for the gauge is in the cylinder head (usually passenger side between #2 and #4) the one for the ECM is next to the water neck. The temp sensor will cause it to run rich, but it'll be longer than just a few seconds.

[Matt 4.3 TBI]

It's been my experience that TBI's will run rough at the first startup when it's cold out. I usually just drive it around the block for a minute or so before I take off. If it gets to you, you can put the stock air cleaner with the preheater hose back on while it's cold. Once the engine starts to get to temperature, the coolant heats the intake bores in the manifold and it smooths out.

[imdawrlus]

haha i understand that its going to run sumwhat rough for a few minutes until things heat up, but it didnt do this earlier this winter, or last winter...this is an idle rough enough to allmost stall it....any ideas?? i already bought the temp sensor so i might as well just replace it because its probablly the original one anyways.....

[imdawrlus]

allright well i replaced the temp sensor and that did nothing for the rough idle BUT it did seem to make the truck a lot more "peppy" which is always good....i took the iac out to look at it and it looked fine, so i plugged it into the wire harness and let it hang there and started it.....the engine revved wayyy up (dont worry, i knew it would) and the little "plunger" came out of the iac valve and fell on the floor....i dont know if its normal or not, but i tried to put it back together to see if i could save it but it didnt run right after that.....so i took a ride down to autozone and got a new one, put it in in the parking lot, started it up, and i havent had that problem since......it also hasent been as cold, but so far so good.........

[Matt 4.3 TBI]

Whoops, not supposed to energize the IAC without it installed in the TBI. It will hit a stop inside which prevents the plunger from falling off.

I usually notice a pretty bad cold idle when it gets below about 45 degrees. The engine will bog pretty hard for the first minute or so until it starts to warm up. I know I could fix it by just putting the stock intake back on...but I can live with the minute of warm up as opposed to the restrictive stocker intake.

[imdawrlus]

FOUND THE PROBLEM!!! i was out checking the spark plugs and plug wires and i put my hand on the distributor and wiggled it just for the hell of it.....AND IT MOVED!! so now i have to wait for my neighbor to get home so i can steal his timing light....this is the second time the distributor has become loose since i've owned the truck........i'll let u know how it turns out..........

[bvr775]

pull the bolt out and put some loctight on it. You make have to throw on a couple of lock washer as well.

[imdawrlus]

this leads me to a timing question....i've done timeing before and i know to disconnect the wire to set the base timing.....above the damper/crank pulley theres a little marker.....it has three "notches and valleys" on it....does one notch mean 1 degree? and then next "valley" mean 2 degrees and so on? haha how far should i advance??? thanks

[Matt 4.3 TBI]

It's marked, might need to take a close look with a flashlight. The first 'valley' is 0, the first 'notch' is 4, next one is 8, last one is 12.
As far as advancing, you can advance it as long as it doesn't start detonating. 4 should be good, but listen to it while you're driving. If you hear some pinging you should back it down a bit.

[imdawrlus]

i advanced it to about 4 and checked for pinging......i would open the throttle up real fast and close it real fast while i had the parking break on and it in drive.....i was standing right next to the hood when i was doing this and i could hear a "knock" as if someone was hitting the block with a hammer........i fiddled with it for a little while and i couldent get it to stop....so i eventually gave up and just put it right back to "0".....it even did it there.....i'm just going to wait until the summer to screw with it again........

[Matt 4.3 TBI]

The best way to check for pinging is while driving. Puts the engine under full load, and has less stress on the drivetrain than what you're describing. Can you better describe that 'knock'? High-pitched metallic sound, or low, heavy thudding?

[imdawrlus]

i'd say its probablly a lower knock....like someones tapping on the block with a hammer......i'm starting to think its somethng other than a "knock" becaue it does it even when i set it to stock.....maby a motor mount....

[imdawrlus]

does this sound like a knock....if not what exactlly does it sound like......also, my mileage is back to usual since i fixed the timing......i also tried changing my driving habbits, 70 on the highway instead of 80, and it seems to have made a difference...since i fixed the timing and changed habbits at the same time, i dont know what do give credit to....but it dosent matter anyways as long as i'm getting 22 mpg's.......

[Matt 4.3 TBI]

It's really hard to say without hearing it firsthand. Could be an exhaust leak at any of the 6 ports, or where the headers bolt to the y-pipe, or at the EGR valve. Could also be a motor mount tapping the frame. A mechanic's stethoscope and flashlight can help you track it down.

[Matt 4.3 TBI]

Almost forgot- if you don't have a stethscope a length of hose held to your ear will work just as well.

[mattownsa97withmafproblem]

yeah i've got an idle problem to especially when i put her into gear it drops to almost the point of stalling and so on and so on throught all the gears except netural however once i run throught them once then everything is fine i have an 02 s dime automatic 4.3 any ideas has to what's going on?

[bvr775]

low metalic thud in the engine?... How many miles did you say you have? over 150K your berings may be worn, but it seen it in the pre96 4/3s as low as 90K. Berings are dirt cheap and worst case you'll need a cranck kit (around $150 and comes with cranck and rod berings).

get you a steth and probe around the oil pan and rear main. prob the inspection plate as well. A loose convertor has allmost the same sound.