Starting and Idling Questions

[AJT944]

Hey Guys -

I'll try to keep this short, but I've gone through my 1986 NA 5-Speed and replaced just about everything rubber in my motor - Every vacuum line, as well as a new DME from F9Tech, and new AOS seals and Idle Control Valve and all of the hoses around those. Also, the Water pump, timing belt, and balance shaft seals and such too. New battery to top it off.

Car started and ran great last fall, and even started and ran great just a few days ago. It fully passed emissions too! Something happened on the drive home, however, and it started running rough and I'm getting a lot of engine vibration.

My question - I know that I have a small exhaust leak - is it possible that got worse? Or do I just have a bunch of old bad gas running through the motor right now that's causing it to run rough? It'll even start and then die now if I give it gas.

What am I missing?

[Matt at Pelican Parts]

Hi AJT944,

Does the car run okay under throttle or is this issue only at idle/cold starts? I'm just curious if maybe the IAC valve may need cleaning if it's been sitting since last fall.

[AJT944]

Hey Matt,

Basically everything sat all winter while I was doing all of this work. The Idle Control Valve is brand new, however.

It runs slightly better at throttle, but is definitely not happy at idle and has a shake at idle.

Seems to run slightly better on some starting fluid, which makes me think maybe it's just bad gas?

[Monkey Wrench]

bad gas can cause poor running but so can so many other things..
maybe clean the distributor cap, see if any of the new hoses came off, If an injector stopped working that might make the engine shake.

Id say the most obvious is that a plug wire might have worked loose, first make sure you don't have one thats just off it's plug..


you could try to get it running unplug one spark plug lead at a time or each injector, either should cause the engine to slow or shake, if you find one that does not cause a difference then that's a clue.

an exhaust leak will cause sound, but that's unlikely to cause the poor running condition you describe.. a vacuum leak can, you might have a loose intake manifold?

gas is easy to change, just siphon it add more and try if its super old gas. you can always dump it back in. a bit of fuel conditioner helps if you park a long time. if you know you will be parking it I'd buy the best gas (highest octane) you can get for that last tank. if you siphon to a Jerry can you can have a look-see for water in the bottom of can.


you might pull each plug and have a look , se if any one is different from the rest.

fuel starvation might be noticeable if it seems to choke when its burning more fuel , you can check the flow rate, see if the pump is moving the fuel ok, there is a procedure in the manual. in case the screen in your tank plugged up or similar.

the idle air valve can be checked out.. it opens and closes, you might squirt some cleaner in and try connecting it to see if it opens and closes. i seem to remember trick for checking them where you can squeeze off the hose, thought maybe if it's hard to get to you can look into that.

maybe if it should be closed and you squeeze the hose then you should see no difference and if you did it proves its open or stuck or leaking air.

is there a closed throttle switch? maybe it can be adjusted or checked if there is one.. i'm wondering if that's related to the IAC wiring, others may know if there is a micro switch that tells the car that the throttle plate is closed , IE it's idling, not under throttle. it might look like throttle position sensor, not sure.

see how I stuck a question in there ? ;-)

[AJT944]

Thanks - I'll check the plug thing.

Fuel filter is new too, as well as all new lines and fuel rail. I had the injectors cleaned a while ago, but maybe they have clogged since?

I'm going to try the plug thing tonight as well as buying some PET injector cleaners and octane boosters into the tank to try and stablize it all at least until I can get fresh fuel into it.

[walfreyydo]

You should check if the vibration you are getting is a misfire - the car could be running on 3 cylinders. Multiple ways you can check this if you google/youtube (including using a thermo gun on the exhaust runners).

If you do indeed have a misfire on one cylinder, you should look at the cap/rotor, plugs or plug wires. Plug wires in particular can be easy to get in the wrong firing order, so double check.

[AJT944]

SOLVED! You guys are spot on! No change in engine when I pulled the plug on cylinder number 1.

New spark plugs, wires, distributor, and rotor on the way

[Matt at Pelican Parts]

Awesome! Good to hear you figured it out so quickly! Keep us updated on how the new parts install goes!

[Monkey Wrench]

I had similar issues with my 88 Volvo. turned out to be a stuck closed or plugged up fuel injector..

I made a post a while back showing how I had created a pressure bottle so I could backflush them and then check their operation visually with them out of the car.. Its a bit long and wordy but if you scroll down you can see a pic of the thing I created..

cleaning your own fuel injectors.

the other way is to pull the fuel rail out, reconnect any wires, put a clean cloth under each injector.

give it a short burst with the starter and you should see some fuel spray out of each injector,, and then with key off the fuel flow should stop right away , if the injector is stuck open it will keep spraying gas until the fuel rail is empty of back-pressure.. if you see one has no fuel on the cloth then its probably stuck closed or plugged up. If you find that symptom you could return some of those parts because that could be the reason for no firing in one cylinder.

might run on 3 because of no spark, it can also not fire on that cylinder because of no fuel, since you ordered parts already you might check if you have fuel flow from that injector.. If you dont have any I'd order at minimum the 4, O rings they are about a dollar each or so , put oil on them so you dont have to fight to get the fuel rail inserted . if not done I'd replace the Pintels on the injectors, and there are some little washers , they are cheap to replace, but I think you said you did replace or clean them above.. maybe you have a used spare onhand..

be very careful and take all necessary precautions if you fire the injectors with them removed.. as it does involve spraying fuel so maybe take the car outside if you do and have an extinguisher rated for a fuel fire handy just in case.. There are other safer means of testing , you can send them out to be cleaned or replace one as a test. or swap them to see if the issue moves.

if you can connect a pressure gauge to the fuel rail you can read the actual fuel pressure. there is a fuel pressure regulator on the fuel rail, it wiil have a vacuum hose, when they get old they have a rubber diaphragm that can leak so if you check that vacuum line and find fuel in it then it means it is probably bad.. if you turn the key off the fuel rail is supposed ot retain pressue so you can see if it leaks down or if it is able to hold pressure for a while as it should.
- I do not think this is the issue at hand since you isolated the issue to one dead cylinder and we are looking for the cause, so not trying to go off on some other tangent..

my 944 also sat and the fuel tank hose leaked out all the fuel , the hoe just outside the tank rotted, so id examiine yours because if the whole tank leaks like that it can cause a massive fire..

what followed was thick brown goo, if you have stuff like that in the gas tank then it could come back to haunt you.

mine is early 85 so it has a metal tank and a fuel screen inside the tank and the hose that feeds the pum is underneath. the plastic screen just inside the tank can degrade or plug, yours probably has the plastic tank so I'm not clear on if it has the same screen but may have one..

if you think you have goo in the bottom of the tank you might check that out..
I noticed on one website they have a cheap one use tool to clean the bottom of the tank , a flexible plastic "scrubbie thing " with a pad for cleaning the bottom of the tank through the fuel level sender hole. you may improvise maybe a pad on a piece of stiff flexible wire could be bent how you like.. like a hunk of round 3 wire romex.. I taped a strong little magnet to a hunk and find it a handy tool to retrieve parts I drop etc. I can roll it up to fit my toolbox or bend it any way I like to puck up fasteners I drop in cramped spaces..

i want to clean my tank so I was planning to put a bucket of solvent under the tank, unhook the hose and use an old fuel pump to recirculate solvent back through the hole for the fuel guage sender, I can leave it run for a while,, to try to wash out any of that tar like crap from the bottom of the tank.
I'm going to do that before even trying to start an of course change the fuel filter.

if you do find a stuck injector , that may or may not mean you have dirty crud being pumped into it.. If so it could re-ocurr.. I dont know how much a new distributor is, I think that the distributor itself is fairly unlikely to be the cause. bad wire seems more likely..

what some do is try cranking int he dark, if the plug leads spark to the engine externally you may see that by the light produced by the spark if it's dark.

Ive seen plugs crack , its rare but I have found a couple where the little porcelain insulator cracked and so the spark could jump from the center electrode to the plug itself without sparking at the end electrode as expected.. possibly cause by a leaky head gasket, symptoms of that are causing weird temperature changes.. water in a cylinder, water coming out the tailpipe, water reservoir mysteriously going low. temperature fluctuations.


Ive seem cheap plug wires that come apart inside the boot where it plugs on to the plug . i found one where somehow one of those things that can unscrew off the end of a sparkplug was already stuck in the wire, preventing it from clipping on to the one on the plug already.. on some plugs they unscrew on some they are permanent. i just had to look inside to see it already had one stuck up inside there..

same with distributor caps. Ive seen where water seemed to collect in that top dibit, then the wire inserted I guess went unnoticed.. so the point is if you unplug the plug wires from the cap , take a flashlight and actually look down upon the cap see if any of the plug lead holes are full of "green" stuff and all corroded.. easy to not see that , if you actually take a moment to look you should see them all clean. that can cause a no fire on 1 cylinder.

often the cap gets dirty you can scrape the contacts with a long thin knife to clean them,, some of the new ones are junk the OEM or better ones will still have copper, if they are some white metal they are junk and will probably work fine but wont last long. i think I paid 70 bucks for a decent one so I'll scrape clean them before I chuck them.. if they get worn then replace.

sometimes the leads are faulty, and spark right through their shielding.. some of the cheap made in china leads are just such junk. Ive ordered them before from other suppliers and basically just thrown them out as soon as I saw what cheap junk they were.


under the cap , sometimes you can have carbon tracking, the spark can jump to the body of the distributor just because the inside of the cap is oily or unclean.. it can leave a track of carbon if they do.. i wash the leads and cap with alcohol to degrease them. that could cause the same symptom, so you could watch for that..

If you just want to replace parts Id try one at a time and if it solves things. Put the bad one back and see the problem return, then you can be more assured you found the actual issue so you can trust your repair more..

[originalowner]

Originally Posted by AJT944

SOLVED! You guys are spot on! No change in engine when I pulled the plug on cylinder number 1.

New spark plugs, wires, distributor, and rotor on the way

Make sure the fuel injector connector is plugged on well.