3.8 rough idle

[OldsPower]

Hi.

i am a new member here, and i'd like to ask if anyone can help me out. looking at my screen name, obviously i'm a GM man, my daily car being a '93 Cutlass Supreme SL, however, i do also own a '87 Thunderbird, and i'm having a few engine issues with this car. i know this isn't a tbird message board, but mustangs had the same engine.

the car is a '87 Thunderbird, 3.8 with fuel injection, and 4 speed auto.
anyways, this engine idles like crap. it isn't uneven and the engine never stalls, but the idle is very rough, sometimes causing the whole car to shake quite violently. also, the throttle response is horrible, this engine is very sluggush. full throttle is required to pass or merge on to freeways.

i've changed the spark plugs, plug wires, the dis cap, pcv valve, air and fuel filters, a new exhaust including cat, and cleaned the egr valve as well as i can. any ideas on what could cause these problems? a bad fuel injector? the car sat for an extended period of time before i aquired it. also, i've never recieved any codes, the ses light has never lit up

i also have another problem, the the trans "hunts" between 3rd and 4th at speeds between 40-50 mph. is that common on these cars or not? i have dropped the pan and changed the filter.


thanks for any help you can provide

 

[GREENBIOCH]

sounds like you have done alot of what you should do to smooth out the idle. But I find these cars idle a bit rough in the first place . Anyways, the person you should talk to about this is on www.v6power.net post in there, there is a guy with a screen name sprout he actually swapped a tbird motor into his sn95 stang, and knows alot about these motors. sorry couldn't help.

one thing I noticed is you didn't change the coil pack, that might be worth a try as well, plus if it sat for a long time, maybe bad gas??

 

[97v6Silver]

maybe the engine needs a rebuild

 

[cobra232]

Hi.

i am a new member here, and i'd like to ask if anyone can help me out. looking at my screen name, obviously i'm a GM man, my daily car being a '93 Cutlass Supreme SL, however, i do also own a '87 Thunderbird, and i'm having a few engine issues with this car. i know this isn't a tbird message board, but mustangs had the same engine.

the car is a '87 Thunderbird, 3.8 with fuel injection, and 4 speed auto.
anyways, this engine idles like crap. it isn't uneven and the engine never stalls, but the idle is very rough, sometimes causing the whole car to shake quite violently. also, the throttle response is horrible, this engine is very sluggush. full throttle is required to pass or merge on to freeways.

i've changed the spark plugs, plug wires, the dis cap, pcv valve, air and fuel filters, a new exhaust including cat, and cleaned the egr valve as well as i can. any ideas on what could cause these problems? a bad fuel injector? the car sat for an extended period of time before i aquired it. also, i've never recieved any codes, the ses light has never lit up

i also have another problem, the the trans "hunts" between 3rd and 4th at speeds between 40-50 mph. is that common on these cars or not? i have dropped the pan and changed the filter.


thanks for any help you can provide

do a compression test. you can get a tester at advance or other auto parts stores pretty cheap. anything from 125psi and up to about 160psi is fine. anything below 125psi isn`t good.

if it`s not an injector which i doubt because it would likely throw a code, it`s a bad piston or headgasket. either of the 2 will cause a rough idle and real sluggish power and wont throw a code. i lost #6 cylinder compression recently on my procharged 98 and it idles the same way and shakes like a paint mixer.

it shows 150psi on 5 cylinders and only 80psi on #6

do a compression test and have a leakdown test done on it.

have the tranny flushed by a good tranny shop and have them add a bottle of either Lucas transmission conditioner or MOA tranny conditioner. a pan drop and filter change wont make a difference but a flush may. have the tranny shop check the line pressure on the tranny too just to be sure it doesn`t need rebuilt

the car may have sat for a while because the former owner knew the headgasket was blown and didn`t tell you. blown head gaskets are pretty commom on the older 3.8`s

 

[94 3.8l stang]

Cobra, You beat me too it. LOL . Thats what i was going to say, try everything he said, and check your wire connections on the Intake sensor. Possibly not metering the air or there could possibly be a break in the line. Look and listen for a Vacuum leak possibly. . Compression would be my guess too. its getting to be an older car, how many miles is on it, you didn't specify, so thats just a guess like i said. I've noticed before too on the older ford engines from the 80 thats the idle is always hunting, for like a month after you reset the computer, then they find a cool place to stay. I think thats from primitive technology though. . Good luck

 

[OldsPower]

thanks for the responses guys

a compression check does sound like a good idea. the previous owner told me the head gaskets were changed, however. the car has approx. 88XXX miles on it. i really don't think its a head gasket, because there is no evdience of oil and coolant mixing, but you never know. when i have some spare time i'll run a comp check

thanks for the help

 

[OldsPower]

one thing I noticed is you didn't change the coil pack, that might be worth a try as well, plus if it sat for a long time, maybe bad gas??

this car doesn't have coil packs, it has a distributor


i've ran a few tanks of fresh gas through it and changed the fuel filter

thanks for your help

 

[77sleeper]

sounds like it could also be a clogged cat

 

[mustang50v8]

one thing I noticed is you didn't change the coil pack, that might be worth a try as well, plus if it sat for a long time, maybe bad gas??

actually, im pretty sure that most of the 3.8's that were older than 94 had distributer's some of the 94's had distributers some had coil packs. my friend who is a mechanic says he had worked on a bunch of 94 mustangs that had distributers and then mine is a 94 but i have a coil pack. but then again mine also had OBDII and suposedly its not supposed to. any my just my info, sorry its off topic.

 

[GREENBIOCH]

Yeah you guys are right, sorry I still think of them the same but the tbirds did have a distributor, its ours that our DIS.

 

[OldsPower]

the cat is newer

i highly doubt the engine is running rich. i could be wrong, but the exhaust isn't black unless you mash the throttle when the engine is cold, the exhaust doesn't smell like fuel or rotten eggs, and the car gets well over 20 mpg, which i think is great for a 17 year old car.