A bad TPS is a strong possibility. You can test the TPS pretty easily using a voltmeter. A digital multimeter is fine. An analog voltmeter is even better. Just measure the voltage between the dark blue (wiper) and black (ground) wires at the TPS. With the engine off and ignition in RUN, slowly advance the throttle from idle to wide open while looking for smooth change in voltage (from almost zero to about 5 vdc). Any erratic change in voltage is a pretty good clue that the TP is bad.
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10:51 PM
blazin' Member
Posts: 1294 From: Yorkton, SK Registered: Oct 2001
Its not the TPS. I have the same exact problem and I replaced the TPS as well as the plugs, wires, dist cap, Ign coil, pick up coil, Rotor, Ignition module, Air intake sensor, O2 sensor, MAP sensor, sprayed throttle cleaner down IAC and throttle body, Tried Fuel additive injector cleaner, and checked for vacuum leak with no results. I think this problem could still be vacuum related even though I have yet to find it or possibly fuel injector related. If anyone successfully fixed this problem please add your input. I am also waiting for a cure.
Maybe its the EGR tube (hairline fracture possibly).
I had a simular problem about a year ago with my 87 GT (the car would stumble on acceleration (only when cold though) and would take like 3mins. before I could move the car when cold or it would stall). It did this from the day I bought it. I threw everythihng at it I could think of (wires, plugs, fuel filter, air cleaner, o2 sensor, injector cleaner, coil, control module) Well about 2 months after buying the car (and living with this problem) the car just died one day (luckily it happened right up the street from my house). I got it home and troubleshooted the cause for it's sudden death (had spark...must be fuel related I thought). took off the air tube sprayed some gas in the throttle boby and it fired. I then pulled the fuel filter to determine where the fuel problem was coming from. Well I didn't get any fuel from the filter when I cranked it over (must be a pump problem). I replaced the fuel pump (after checking the pump fuse) and after installed it fired right up. As an added bonus my poor cold starting and cold stumbling problem was now cured as well (it has been fine since)!
I think what hapened was the pump was slowly dying and these were the warning signs of it. I am in no way suggesting to replace the fuel pump (it may not be your problem) but it was mine!
Good luck!
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12:55 AM
Standard Member
Posts: 4667 From: St. Cloud, MN Registered: Apr 99
crikey.. my quad has been doing this lately. At first it was the fuel pressure regulater. Replaced that and everything was fine for a little while, but now stumbles and 'chuggles' if I don't warm it up for a few minutes before driving. Cleaned out the throttle body, replaced coils.. next try is new plug boots and maybe a coil housing.
If those don't work, I'm guessing leaky or bad fuel injector or fuel pump going bad. Fuel injectors are easy to get to for me.. fuel pump I don't even want to deal with.. <sigh>
------------------ 1988 Quad 4 Coupe 5 speed More pics of the coupe 1986 GT 5 speed, 1984 SC Auto AOL: LastMinuteBastrd AIM: SavedbyJebus
I replaced the fuel pump for my 4 to 6 conversion and didnt buy a new one. I just got a used. Now I am left this new possibilty to contemplate. I sure hope that isn't it but my car is exactly the same way right now when cold.
I would say chances are if after replacing the fuel pump (even though the one used to repace it was not a brand new one) that chances are there is something else causing your trouble (what are the chances of 2 pumps both being bad). I think in my case I just got lucky (although I don't know if I can say I was all that lucky concidering I had a heck of a time replacing the old pump on my car). It just so happened that the pump died and after I replaced the pump my poor running condition was fixed (so I contributed it to the pump).
If it is a vacuum problem good luck finding it. The other thing I would check is the injectors (as you already mentioned).
I would perform a leak down test on the injectors to see if the injector(s) are leaking. This could explain poor cold starting. You may also be able to tell if the injectors are leaking if your car has a heavy gas odor when it fires when cold (cylinders may be flooded). I'm not sure if a leaky injector could cause a stumble on acceleration though but would cause poor cold starting.
I will be watching this thread with interest. I've got an '85 SE, V6, auto, which also has problems with off-idle hesitation, esp. when cold.
The car seems to run very rich (exhaust smells strongly of gas) when running in open-loop. Sometimes, when the engine isn't thoroughly warmed up and I shut it off, I get a hard restart.
Timing is at 10° (factory spec) at both 1 and 4 cylinders.
I do plan to replace the fuel filter relatively soon (according to the previous owner's maintenance log, it's never been done).
Thanks!
Ed
Edit: Added engine/tranny info.
[This message has been edited by edhering (edited 09-26-2002).]
I blew thru the new filter before putting it on--almost as easy as exhaling normally.
Took a long test drive. Throttle response is more crisp. According to the "butt-o-meter" the acceleration feels snappier, but this is entirely subjective. I don't think I picked up much, if any, horsepower or torque, but the fuel delivery is working better than it was.
When I got home, I tried blowing through the old fuel filter. Even accounting for the fact that the new one was dry when I tried it, and the old was wet, it was still much harder to blow air through the old one than it was to blow air through the new one.
As I say, the throttle response is better than it was. I get better throttle through the corners, too, and overall the car just feels like it's performing better. (But I think "better", in this case, merely means "up to par".)
Does it solve your cold start hesitation problems? I also just wanted to mention that I also have replaced the fuel filter when I had the engine out, but without improvement.
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09:00 AM
blazin' Member
Posts: 1294 From: Yorkton, SK Registered: Oct 2001
Cold start and/or cold running problems could be related to the cold start injector too.
I have battled the problem for 5 years and have gotten rid of nearly all sign, although occasionally it does come back. At least it doesn't stall out, and usually settles into a smooth idle within 30 seconds to one minute.
What didn't work: Curing vacumn leaks. They were causing problems of their own, a pair of cracked lines, a bad EGR tube. Replaced both, along with a new EGR valve. No more code 32, but still had the rough cold start/idle.
Next I went after sensors (some neededreplacement anyway). Cold air charge sensor (in air-box), coolant temp sensor for ECM (different than for guarge), TPS, and MAP, O2 (I was getting the O2 sensor code when I replaced it). I felt the car ran a little better, but it didn't really help.
I also replaced the fuel filter, no help in cold idle.
What did help: On the recomendation of my uncle (he's a mechanic) I sprayed carb cleaner into the throttle, cleaned it out with a tooth brush, and that helped some. Next I sprayed the can in with the engine on (it burns it away) to clean the whole intake track out a little. This seemed to help a lot. I did put the whole can thru. Later, a new IAC valve did the job in stopping the stalling problem I would have right after starting. Some fuel injector cleaner into a tank full of gas and now the car runs fairly well.
I still get a little stumbling cold, and its a little hestitant for a minute or so. It runs very rich when cold too, and I feel fairly positive its the cold start injector, or the other injectors leaking extra fuel into the cylinders. Since its only when cold, the cold start is my main suspect.
I also had a partially clogged cat-converter which also contributed its own driveability problems.
Take the info as you want... since my situation might be a little different than others. However, it seems that gummed up systems were causing most of the problems, and cleaning it all out was the answer!
I did the spraying cleaner into the throttle body while running trick which did seem to help a little. But not enough to suit me. I sprayed only about a 1/4 of the can into the throttle body and IAC inlet. Should I spray more? Also did you replace the IAC sensor (whatever the electronic part is) or do you mean the IAC itself. I was looking at the throttle body and the IAC seems to be one with the throttle body. How would it come apart????
I want this car to run like new. And it should run like new with all the new parts. SHoot its more new than it is old.
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01:16 PM
Fformula88 Member
Posts: 7891 From: Buffalo, NY Registered: Mar 2000
I replaced the IAC valve. Its the one right under the TPS. Inside, its a pointed rod that either opens or plugs the air inlet you can see infront of the butterfly in the throttle to control idle speed.
Its definately worth it to take it out and at least clean it up. After doing this I didn't think it was working so I replaced it and did notice a difference after the computer reset (you have to drive over 30 or something like that to reset it).
I suspect that the biggest contributor on mine at this point is the fuel delivery somehow, but have also wondered if the vacumn lines have gotten gummed up inside restricting airflow based on the amount of crud in the intake manifold and throttle.
Originally posted by connecticutFIERO: Does it solve your cold start hesitation problems? I also just wanted to mention that I also have replaced the fuel filter when I had the engine out, but without improvement.
Well, it didn't fix mine. As I said it made the throttle response better, but when it's cold the thing still has a tendency to chug or hesitate. I too am wondering if perhaps the cold start valve is involved with this problem.
The hesitation/chug problem is better than it was, so I now know that fuel delivery was part of the problem--but it's apparently not all.
I've been thinking, tho--if the fuel filter was clogged, what must the in-tank filter be like? Perhaps my next step will be to drop the tank and replace the pump and in-tank filter. And, incidentally, also to clean the tank out, if possible....
What can you do for the cold-start injector? Clean it? Or just replace it?
okay, i was reading further down the forum list about everyone having hesitation upon acceleration, stumbling on cold start, bad idle, well my car does the same and has been for quite some time. it'll even sometimes sound great on initial start but the longer i let it sit, the grumblier and weaker it'll get until it'll finally just die. now i have also obtained another weird quark. when making 90 degree turns at faster speeds i loose all response for about a second or two before acceleration and throttle pick back up. are the 2 symptoms related? any ideas?
