StupEd05

Occasionally when I get in the car and the engine is cold I will start it up and it runs and idles great, but when I back out and put it in 1st and start to move SOMETIMES it sounds like it drops a cylinder for a little bit. To get rid of it I usually just have to rev the engine a tad or just let it warm it up, sometimes it seem as though right when the engine hits temp it goes away. Usually it just requires a little rev and Im on my way. Has never really gotten to me just a little annoyance I would like to get rid of if possible.

testarossa_td

Start cheap go o2 sensor. I believe yours is the one wire. IF you don't know when it was last changed change it.-check one of my old posts to see what it can look like.

Bottom line is it needs to heat up before it becomes remotely effective.

StupEd05

Lol, that could be it, the connector on my O2 sensor broke with the PO so it isnt even connected. Maybe to time to fix it eh? The O2 sensor changes A/F ratio even on a cold start right?

testarossa_td

On cold start it really provides no value at all.
I have a '86 951 and it will run kind of rough for a couple of minutes and it has a heated three wire o2 sensor.
I have a Air/Fuel/Duty meter that helps me visualize what is going on with the o2 sensor.

Fishey

Change your sparkplugs and it will be fixed. (could be plugwires/rotor/cap/coil) but 99% of the time its sparkplugs. Get champion coppers they work great! (Stay away from platniums)

02 sensor will do nothing for it because when the engine is cold 02 sensor isnt even working. If the problem was when the engine is hot then I could understand it being an 02 sensor but when cold it cannot be a 02 sensor.

Zero10

I had this problem on my 86, chased it and chased it. Never found it.

I changed plugs, cap, rotor, wires, then removed and cleaned all 4 injectors, to no avail.

None of the spark plugs showed abnormal coloring or anything to indicate which cylinder the problem was on. Mine would run on 3 cylinders for about 30-45 seconds on really cold starts (below freezing).

StupEd05

It seems to idle fine, unless it is really cold out like this morning. This morning when I went out it started up and I have it set to idle at 1k, but sometimes it drops, for instance it will kinda die down to 500 and shoot back up to 1k and it does it about every 5 secs. Once I give it gas its fine. Another thing about the running on 3 cylinders bit is that I have gotten out when I was running rough and pulled plugs to see what cylinder it is and each time it varies so I doubt it is an injector sticking or any specific plug wire. Another example would be sometimes I will drive for about a mile or so and then If I am in too high of a gear it will drop a cylinder, like if im in 3rd going 25-30 and give it too much gas it drops a cylinder, so I have a feeling its something to do with the A/F ratio being way off when its cold. Once the engine is warm or I have gotten it to go away it wont come back. I.E. say i get in and it does it, I rev and get it to go away I could then drive for 5 hours without ANY problems at all. So in other words, what controls A/F ratio during a cold start?

EDIT: I have replaced Cap & Rotor, plugs, and wires and cleaned and resealed the injectors.

StupEd05

bumpity...

testarossa_td

My only recommendation would be to buy an o2(air fuel) meter.
That might help you better understand it.-and other problems down the line.
Just buy a cheapy one, and when you are done with it, sell it on ebay , or give it away
If you want the full duty meter as well, that costs more and go to Lindseyracing.com for that. These are just fun diagnostic tools that help you better understand some of the fun stuff you car can do at different times of your ownership.

testarossa_td

Here are my two previous posts that might gain you some insight...or not.
Sounds similar to some of your problems...or the start of.

https://rennlist.com/forums/924-931-944-951-968-forum/182500-throttle-position-switch-86-951-long-story.html

And what my o2 looked like-that contributed to some of the other posts problems.

https://rennlist.com/forums/924-931-944-951-968-forum/181991-164k-o2-sensor-86-951-a.html

StupEd05

Wow, thanks alot for the links. very interesting. I am ordering an o2 sensor over the weekend. Might not fix this problem but needed nonetheless.

testarossa_td

Not a problem. Just go to Autozone, they almost always have them in stock.
And yours is only one wire so it should be really cheap.
Do an advanced search on rennlist to find out more detailed info.(part number etc..)

tomc_85.5_944

I have the exact same "three or less when cold, give it a tiny bit of gas for 30 sec, and it goes away" problem. Keep us posted on whether the O2 solved it. Got 150k on mine and original O2. Please also post up if replacement made a difference anywhere else.

Too much other stuff going on to try to mess with it lately.....

Thanks!

StupEd05

I havent gotten to the O2 sensor thingy yet as I just noticed the wiring harness I put in is missing the O2 plug, the green wire it there though so I guess Im gonna have to jimmy-rig it. I think others are right though, that should only help in a warm situation. It hadnt done it for a while till today, it did it really bad. Started up fine, pull out of parking space drive for about 10 secs give a little too much gas and bam drops prolly 2 cyls, and loses power and after jackin with it it died, started back up gave it gas for quite a while goes away and drove strong as ever. I am starting to think that the temp sensor to the AFM might be to blame. Anyone know how this works??? Seems to do it a LOT more when below freezing or really hot say the 80's to 90's. The afm is the only thing I can think of that alters the a/f ratio right at start up, in fact, when it died today it was extremely hard to start back up without giving pressing the gas, as soon as I touch the pedal it fired off, making me think maybe there is a bad spot on my AFM track or something in the AFM is fudged up.

Anyone with this problem try a new AFM???

testarossa_td

The Air temp sensor as you know is part of the Air Flow Meter-thus non servicable. I agree with your logic as far as cold start= o2 sensor's value null.
The problem I was having was similar(as stated before) and was in part related to the AFM. In addition to o2 sensor and the straw that broke the camels back TPS! So if possible, simply find a cheap AFM replacement(plenty on ebay or at 44andmoreparts.com) and go from there. Eventually(and theoretically you will need your o2 sensor back). The nice thing about these cars is that there are tons out there and replacement parts are readily available so cost should not prohibit you from R&R'ing most components.
And for fun once the problem is gone, you can replace the parts in reverse and see what actually was the problem. Plus you can put your parts on ebay or give them to someone who wants to play with them.