madening rough idle

[Mac]

my tercel, despite me rebuilding the carb, replacing all the vacuum hoses, and quasi-rebuilding the engine and replacing the valves, still idles terribly.

last night i swapped out my ignition coil for a spare i had, hoping that would fix my idle, but it seemingly made it run worse, so i bought a new one at work today and it runs the same. which leads me to believe it was the vacuum hoses i replaced (again) last night at the same time as swapping the coil last night, i figure its something i did and not the hoses themselves.

anyways, i just spent a good half hour looking at it and i figure my problem is caused by two things:

1.extremely lean running at idle, the O2 sensor i installed is showing .15V, a far cry from .9V and the diatonic ratio (14.5:1 air/fuel ratio)
causing a rough idle due to insufficient fuel.

2. there is very little combustion going on in number 1 cyl at idle due to the fact 3 main vacuum lines come off its runner and whatever the lines are connected to are leaking and there is alot of air being sucked into number 1 cyl and not fuel. so my 4 cylinder engine is running on 3 cylinders and 1 cylinder is an air pump at idle.

I'm really surprised my idle NOx emissions aren't higher than they are. my solutions i'm going to try are as follows:

1. swap the primary jet (located inside the float bowl) for a secondary jet for the primary venturi from a spare carb i have, effectively increasing the amount of fuel available to burn at idle and probably improving throttle response and acceleration at the same time.

2. block off the vacuum line leading to the EGR stuff as i blocked off my EGR and its more of a source of leaks than anything, and/or re-route the 3 vacuum lines coming off the number 1 cyl intake running to a common source so the vacuum will be shared by ALL cylinders.


I'll tackle problem number 2 on Thursday, check my O2 readings and let you guys know how it goes.

[takza]

Could be:

* no vac advance at idle?

* O2 should be cycling after warm? Mine reads around .8V all the time

* EGR could be leaking some even if no vac to it?

I tried a simple vac setup...just canister...air injection...AAP...but the engine would stall after warming up and then stopping for a short while...wouldn't get gas from idle unless you worked it for awhile...not drivable. Put it back.

[Mac]

funny thing is I'm thinking that me hooking the vac to the dizzy is whats causing the problem (the advance/retard diaphragm is leaking). I'm going to definatley re-route the after-carb vacuum for the distributor to a common source so its not being taken from just the #1 cyl runner, that should help things out quite a bit. then double-check the lines I replaced, and possibly replace the 2 check valves with universal ones.

I never thought the EGR valve could be leaking, so I'll check that out, but the EGR should only be getting vacuum at cruising speeds and not idle. but it certainly won't hurt to look.

[Mac]

well, i checked that all out, re-routed some vacuum lines and it still idles terrible.

I ordered a new distributor from work today, hopefully that will fix things. after that the only money im spending on this engine will be filters, oil and plugs.

[Neu]

well, i checked that all out, re-routed some vacuum lines and it still idles terrible.

I ordered a new distributor from work today, hopefully that will fix things. after that the only money im spending on this engine will be filters, oil and plugs.

you spend a lot of money at work, they must love you

haha

[Mac]

yeah, lol. my boss was saying i probably make less money working at napa because i spend so much there.

[Mac]

so the new distributor did SFA for the idle, and the threads for the cap were pre-stripped so i had to jury-rig it on. awesome. not to mention the advance/retard diaphragm things were pointing the wrong direction.

needless to say i'm going to return the distributor to work as defective and put the old one back on and cap the advance/retard lines again, re-torque the manifolds to the head and then mabey substitute the primary jet with a larger secondary one.

[takza]

Might try redoing the diaphragms inside? Grind the crimp off...or most of it and use light cloth and goop or silicone to rebuild them? Epoxy or ??? to put it back together...

[splatterdog]

One thing to check that hasn't been mentioned is the idle(first fuel cut) solenoid. Stethoscope it while someone turns the key on and there should be a noticeable click. Check both solenoids for comparison.I wouldn't upsize a main jet for idle problems either. Even the smallest main should keep up with the idle circuit.

[4wdchico]

I never thought the EGR valve could be leaking, so I'll check that out, but the EGR should only be getting vacuum at cruising speeds and not idle. but it certainly won't hurt to look.

Looks like you are thinking about the possibility that a EGR valve can leak at the actuating diaphragm. Yes they can leak there, and on a car like the terc that has other emission vac systems that share the same circuit, things can get weird.

But also remember that the EGR valve is always exposed to manifold vac on it's outlet side if the engine is running. So if the pintle shaft (think valve stem) becomes worn in the EGR valve body you will get a vac leak via that route. Vac leaks of that type can be big ones. I have replaced far more EGR valves over the years for pintle leaks than for having leaky diaphragms. I'm actually kind of surprised to find an older car that does not have a pintle shaft vac leak. Easy to check with propane.

[ARCHINSTL]

IF you are thinking of cleaning the EGR valve - at the risk of self-trumpeting...
http://www.tercel4wd.com/forums/viewtop ... f=7&t=1496

I had a leaky EGR modulator and replaced it prior to cleaning the valve (OE-only, $63 in '05, a deal from Butler Toy).
My valve itself held a vac after cleaning, so it is (apparently) OK - plus, the car ran better.
I would strongly suggest using PB Blaster on the nuts prior to attempting to remove them -anti-seize on their replacement - you will definitely need a new gasket (AZ-ADV, etc). Note also that cleaning the old gasket from the manifold mount is REALLY hard.
Tom M

[waynehoc]

1.extremely lean running at idle, the O2 sensor i installed is showing .15V, a far cry from .9V and the diatonic ratio (14.5:1 air/fuel ratio)
causing a rough idle due to insufficient fuel.

Mac, just out of curiosity, my understanding is that manual trans Canadian vehicles do not have a computer nor an O2 sensor. Is your Terc a US model?

[Mac]

the solenoids themselves work, I tested them when i rebuilt the carb, as far as working properly (getting power at the right time) i'm not sure. should i just be listening for a simple click? or something more?

I'll look into the EGR modulator, but I haven't suspected it because unplugging the vacuum lines it didn't seem to do much nor did using an (unlit) propane torch near it.

as far as the O2 sensor, i removed the pipe going from the air cleaner to the exhaust manifold and replaced it with a flange and O2 sensor i got at the junk yard (only $5) so that i could see what the air fuel mixture is.


one funny thing is, if i remove the fuel line coming from the tank to the pump, my idle improved, i would have thought too much fuel if it wasn't for the O2 readings showing lean. mabey this is a sign of the solenoids on the carb acting up?

[Don Jorgensen]

I've been trying to sort out
1. Won't idle with vaccum hoses properly installed.
2. Will idle with hose from the top of the carb horn bypassed to carb base and split to original port.

Now the gas mileage is really poor, I hate to say how bad. Yes the dist vaccum advance is working as well as the advance.
the idle is smooth but every 5 or 7 seconds, it misses a beat.

Runs great on acceleration but surges when slowing down in gear at any rpm

I've been switching out the solenoids...I have 3 carbs same issue with any of the 3 installed. The solenoid that is facing the firewall only clicks when the a/c is on or the cooling fan is on. I tested off the battery and it clicks but unpluging and repluging the terminal with the key on and a/c off generates no click

These solenoids have an O ring on the end. I'm wondering if fuel is flowing past when the solenoid is off if this O ring is flattened or hardened?
Don

[Mac]

i looked up those solenoids at work.

one is called a fuel cut solenoid, the other is a "idle cut solenoid" I'm guessing it cuts fuel to the secondary at idle or something (and making my car idle like crap right now)

my cost was well over $100 for either