Very rough idle

I have a 93 Tbird, and in the past few months it has started to idle very rough. I changed the plugs, wires, cap, rotor, pcv, and nothing seems to help. It almost seems like its missing on one cylinder. When I add just a little power (near 1000rpm) it smooths out??? Anyone have a simular problem?

I have a similar problem in my 89 Bird. My idle is only slightly rough. I posted a thread I was tolded I should check the compression in the cylinders or something to that affect.

I never did this because the slightly rough idle was bearly detecable, and it didnt happen on a regular occurance. But that may be a good next step for you seeing as you have already given you Bird a complete tune up.

possible o2 sensor.

I have a 93 Tbird SC and have the same problem. I have changed the plugs, plug wires, new coil pack, and had my DIS tested and it was fine. I pulled the wires from the DIS to the coil pack and they tested good. On the coil pack, 1-5,6-2, and 3-4 fire together. I'm getting no spark at the coil pack for 1 and 5. Have a feeling it electrical. The problem was intermitant and would happen about two times a week, but after the tune up it is happening on a regular basis now. When the car is cold it runs fine for 2-3 minutes then it starts to miss fire i.e. no spark at 1&5. Any ideas? I'm thinking my main computer? I'll keep everyone informed if I find something out.

Todd
93 Thuderbird Super Coupe

Ok so I took my SC to the Ford dealership. They tell me its my DIS. 350 plus 120 install!!!!!! It took my less than 5 minutes to remove it and get it tested at the parts store. It tested fine, but as I have been told by auto parts people... the test can be wrong cause it doesn't test it under normal working conditions. Checked around on prices..... Advance AutoParts was cheepest, Oreily's within $10 and would match, and Napa was in the middle at 165! Plus it was in stock!!!!! All the rest were next day. The guy at Napa said that if your plugs wear down, it will cause the module to burn out (or parts to) My plugs had 80K and had a gap of 70 plus on all. Lesson.... change the plugs even if its a job or $$$$$. I'm putting the new DIS on tonight and I will let you know if it fixes the prob. Otherwise the Ford Dealership got me for $75!!! More to come.........

Well.... my thunder chicken..... is once again a Thunderbird!!!! Problem solved and the new plugs make a difference. Now I can burn rubber again! Hope this can help others.

Todd
93 Thunderbird Super Coupe

planman4y2k, what type of plugs did you go with again? were they pre-gapped??? I have the standard 3.8 V6 Bird, and I went with a set of pre-gapped platinum plugs, and my car still idles slightly rough. its hardly noticable to anyone else, so i'm not going to worry about it to much, "yet". but i was thinking maybe the plugs i went with, "i cant remember the brand name off hand" will not work well with my Bird. I know they are double sided or double "something" platinum, and I think they are by "Bosch".

I just used autolite regular plugs. I like Bosch, but didn't want to spend the $$$ cause I'm going to probably sell the my car in the future. (twins and Tbirds.... not the best mix) I run Bosch in my vette, but I didn't use the plus fours.... just regular bosch plats. A few sprint car buddies told me that the plus fours don't work as well. I know rumor mill but I trust them. I did gap my plugs at .034. Thats what the manual said... so I followed it. Hope this helps.

Todd

P.S. JMT... you get your problem solved?

you may have a slightly plugged or starting to plug converter pay some shop to check the back pressure through the o2 sensor hole pre-converter if its over 1.5 psi at idle you have an exhaust restriction which is probably the converter plugging up or you can take the conveerter off and see if your power comes back but of course it will be louder than hell while u test drive with the converter off

its been my experience (i do this everyday) is to use motorcraft platinum plugs in 3.8 & 3.0 engines--the 3.0 you should also use motorcraft wires saves alot of headaches--refunding money to customers or doing the job over again because you tried to save a couple dollars---most cars plug selection is anyones preference but because of combustion chamber temps different brands of plugs and wires dont seem to perform as well

i agree with coondawg6, use autolite. Bosch plugs may cost more but they are the biggest POS on the planet. every winter we get people coming in with a nostart condition and the first thing we check are the plugs. if theyre bosch we immediately swap them out with ac delco or autolite plugs and 99/100 it fixes their no start problem. fouled plugs. why? look at the porcelain electrode on a bosch plug, its about the size of the lead you use in your mechanical pencil. it tends to snap off VERY easily. all thats left is that same size electrode but flush or down in the porcelain and then all it takes is a tiny droplet of gas to foul it. Also, 3.8L ford headgaskets are NOTORIOUS for blowing. i do at least 4-5 sets a month. quick test is to leave the radiator cap off and start the car(usually cold) if the radiator spits out coolant then you probably need new headgaskets. if you do it yourself its KIND of a chore, the revised headbolt torque sequence is a very good workout.

how many cat. convertors do the 89 TBirds have? My Bird is a standard V6, I dont know if the LX and SC Birds are different.

oh and also, is autolite a brand of ford? when I first noticed the idle problem, i had platinum autolite plugs in. i didnt also had aftermarked wires. but i never had any starting problems, just 6 months after i put in the autolites i noticed the idle problem. thats when i got the bosch-2 plugs from advance autoparts.

i was thinking maybe i had a cat. converter problem or an o2 sensor problem. would a faulty o2 sensor cause an idle problem???

have you ruled out the head gaskets? 3.8s are very notorious for headgaskets. pop off the radiator cap on a cold start, make sure its full and have someone crank it and watch the coolant. careful because sometimes when the headgasket pops its bad enough to push coolant pretty hard outta there. anyway yours might be a small leak that is only at idle which is what im getting at so youll probably only see some bubbling. which if the coolant is stone cold should nto be present.

I still have not figured out the problem, I was reading around and think it could be the Mass Airflow Sensor. or the O2 sensor as someone already mentioned. I have 244,000 miles in the bird and have not replaced any of that yet. The only issue I have really had was a blown head gasket around 150,000. Other than that it works great.
I am thinking its something electrical....

RahX, let me just make sure i understand something. when the engine is cold, i should remove the radiotor cap, than start the car. and if i see bubbles that means the head gasket has blown??? will the bubbles appear immediatly or will i have to wait a few minutes???? i'm gonna check it out based on what i understand. if its a head gasket, the first thing im gonna do is go out and buy a "for sale" sign....

Don't damn the head gasket just yet, the best and easiest ways to tell are 1 by pulling your oil dipstick and looking for a milky frothy mix of oil and coolant, and 2 look at the coolant, if it looks milky and frothy, or is black, then your problem is head gaskets. Alternatively you could have the cooling system pressure tested. I have never seen a blown head gasket just leak at idle, when they go you know it. You said you got pre gapped plugs, I recommend you take them out and check the gaps, and set them to factory specifications. all the MN12 and Fox body birds (except the turbo coupe) to my knowledge have 3 cats, 1 near each manifold and 1 after the Y pipe.

With almost 250K on the clock I'd look pretty hard at the O2 sensors, and take a llok at the injectors as well, the orings could be leaking or the injectors might not be working properly. Resistance in each injector should be between 13.5 and 16 ohms. You can unplug them one by one to check for one being inoperative, idle speed should drop at least 100 RPM momentarily when you unplug the injector. If any do not drop RPM at least that much then its not delivering enough fuel.

wow overl0rd, you gave me alot of meaningful information. i can say, after performing that radiator test, and checking the antifreez and oil, i highly doubt i have a head gasket problem (knock on laptop plastic). i was leaning toward an o2 sensor problem myself. simply because my miles per gallon seem a little low (around 15-17 city). and the exhaust has a funny smell. almost like burning toxic chemicals. another thing ive noticed is that water tends to drip from the tailpipe when the car is idle. someone told me that was normal though.

Rough idle or stalling can be caused by a fouled trottle plate. How does the trottle plate look? I had these problems on a Buick 15 years ago on a 3.8 TBI. Emissions control makes a mess inside there--pull off the air intake hose and take a look. If the late is crapped up, the idle will be affected as well as computer inputs---I venture to say. the cure can be as simple as cleaning the plate area with cloth and toothbrush with cleaner. Careful at that. Otherwise, like in this picture, I took the plate off my vehicle and cleaned it up--first time in 2005 in years.

http://www.MyOnlineImages.com/Members/KATHRED/images/Image029.jpg (http://www.MyOnlineImages.com)

SUERED, i've used throttle body spay to clean the throttle plate not to long ago. but i never took the plate off to clean it. do you think i should? i've heard that SEAFOAM is pretty good at cleaning the throttle plate. ive put some of that stuff in my tank, and oil, and i'm noticing my Bird is running a little better, but the little idle problem is still present. basically i want to eliminate all simple possiblities before i start exploring complex more expensive possiblities. so im goin to check the throttle plate, and change the bosch-2 plugs i currently have in there.

thanks every and happy holidays to all!!!!!!!!!!!!!!!!!

its not 100% but usually if the headgasket pops and you open the cap with the engine stone cold there shouldnt be any bubbling action at all. there might be some slight up/down movement. it also depends on where the headgasket is leaking. if its leaking from a coolant jacket into the cylinder then there wont be any oil, just a lot of bubbling and pressure in the cooling system. if it leaks into an oil passage the oil pressure will force oil into the coolant and maybe coolant into the oil. but re-reading, an idle only problem might be a MAF sensor. you need a tamper proof torx bit or a pair of pliers and some patience. pull it otu and clean the two wires. be GENTLE theyre very very delicate. but they should be silvery. if theres a lot of gunk use some carb cleaner and a paper towel to clean em.

The deal,

I would say that Trottle Body removal is a lot of effort for a simple clean job. I had taken mine off because I had injector problems and did maintanance work on the air intake then. If you believe that your cleaning was sufficient, then I say, forget my idea for now and look at other less drastic measures first to remedy the idle problem. Good luck!