bad idle occurring only while in D at stop light

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this is makin me crazy!!

took the van out this morning, after re-torquing the inlet manifold and TBI bolts last night, it definitely ran better, smoother...but...

all was going well until i had to sit at a stop light for a few minutes and there it reared its head again, rough idle, sat there in Drive, waiting, it came from nowhere??

then when i have to drive away, the thing's running like a bag of wrenches....not as bad as before the torque down but rough all the same.

have changed the fuel and air filters, checked last night (in the dark) for electrical shorting on the ignition system

so, whadya think guys?? what is it about the relationship between the engine and tranny, ie, being in gear, under load, that might affect something to produce a rough idle while sitting there??...this is the first vehicle that i have ever had with an auto tranny so im not well versed on the effects of them on eachother....does the TV cable come into this somewhere??

HEEEEEELLLLLLP
 
I'd check for vacuum leaks, not only where you were working, but everywhere! Spend some time and really check it out.
 
when its in gear it will idle down about 200 rpms or so. i think thats why you only notice it in drive. a vacuum leak would make it idle up. im assuming you dont have a CEL on and you have already changed the plugs, right? every thing i can think of would set a code if it was bad like map, iac, etc. try to hook it up to a code reader anyway and see what happens. you might find something

is there a possibility you have a bad motor mount and are mistaking the roughness for engine miss?
 
The engine is under more load sitting at a stop in D than in Neutral. So a marginal condition somewhere may allow it to idle smooth until you put it in D.
I agree with vacuum leaks since you were just working on it; but an ignition fault can also cause this.
 
IS this TBI or MPFI? at your mileage the throttle shaft may be worn. Dont forget to check the evap system - a lot of air goes in to the intake from there. Also, have you ever replaced the timing chain&gearset? - it would be shot by now. Look for unstable timing light in service mode.
 
Originally Posted By: electrolover
when its in gear it will idle down about 200 rpms or so. i think thats why you only notice it in drive. a vacuum leak would make it idle up. im assuming you dont have a CEL on and you have already changed the plugs, right? every thing i can think of would set a code if it was bad like map, iac, etc. try to hook it up to a code reader anyway and see what happens. you might find something

is there a possibility you have a bad motor mount and are mistaking the roughness for engine miss?


It depends on how bad the vacuum leak is. There are no doubt a number of conditions that can cause it. Vacuum leaks are usually where I start, especially since the OP recently removed some parts from the engine that can leak vacuum leaks. JMO
 
So it was idling okay at a stop light then suddenly got worse? You might have a coil overheating or something wierd like that.

If you hold the brake and give it a touch of gas still in drive does it smooth out? Maybe you stopped with a cold idle that was higher and it settled into a hot, low one?

If you do have say an intake gasket vacuum leak on one corner that will make that corner run worse under low load. Might be time to spray some WD40 or something around the intake valley with the thing idling.
 
you guys are the best!

ok, motor mounts have been changed with OEM parts, the engine is TBI.

check engine light not on but bulb may be bad....will check it!

the plugs, wires, cap & rotor have only done about 5K

timing chain & gearset are a complete unknown, prob factory orig?

a member on the astrosafari forum suggested a TBI rebuild kit which includes a new spring to set fuel pressure regulation??

even though i have re-torqued the TBI and inlet manif', there could still be a bad gasket on one or both??..re-torque might have just lessened the severity of the symptom?
 
Originally Posted By: eljefino
So it was idling okay at a stop light then suddenly got worse? You might have a coil overheating or something wierd like that.

If you hold the brake and give it a touch of gas still in drive does it smooth out? Maybe you stopped with a cold idle that was higher and it settled into a hot, low one?

If you do have say an intake gasket vacuum leak on one corner that will make that corner run worse under low load. Might be time to spray some WD40 or something around the intake valley with the thing idling.


at first, yes, it will idle fine and then it starts playin up...if i move it to N, it doesnt happen....i had wondered about the coil?

it only ever happens when engine is at hot running temp...which is why i thought that the re-torque would help, i was picturing the inlet manifold warping slightly under the heat expansion and allowing a vacuum leak

what is the logic behind the WD40 test??
 
just had another thought....about a year ago, i came to finding that the van had no thermostat in it?!...I fitted a 180 in stead of 195...maybe im now finding out why they took it out in the first place??
 
Originally Posted By: demarpaint
Originally Posted By: electrolover
when its in gear it will idle down about 200 rpms or so. i think thats why you only notice it in drive. a vacuum leak would make it idle up. im assuming you dont have a CEL on and you have already changed the plugs, right? every thing i can think of would set a code if it was bad like map, iac, etc. try to hook it up to a code reader anyway and see what happens. you might find something

is there a possibility you have a bad motor mount and are mistaking the roughness for engine miss?


It depends on how bad the vacuum leak is. There are no doubt a number of conditions that can cause it. Vacuum leaks are usually where I start, especially since the OP recently removed some parts from the engine that can leak vacuum leaks. JMO



your right it is a good place to start. i assumed it was MPI the TBI is not as good at correcting for a vacuum leak so it may well be just that. a man could run over all the lines and then do a spray check with b12 to check the gaskets....
 
Probably a long shot, but something to add to your list--I had a Saturn that developed a low idle, just low enough to make the interior vibrate more. It also felt like it almost wanted to die between gears (manual trans). The EGR valve was sticking open slightly. With your mileage, it might be worth removing the valve to clean it.
 
You always ck vac leaks first in these situations. Cars with a computer controlled idle speed (essentially everything now) can sometimes mess with your diag. Your PCM will compensate as long as it can, then it eventually gives up, and usually sets a code (see where I am going here). Your light doesn't have to be on to have a code. Maybe you have an EGR valve acting up. Pull the air cleaner/TBI bonnet and look at your injector pattern, any drips, oddball spray?

Fuel filters/air filters will NEVER effect idle first. You will notice that on accel first.

Ck you TBI gasket, spray around the intake manifold/gaskets with some carb cleaner to see if the idle smooths out. Quick and dirty way to ck for vac leaks.
 
The idea of spraying WD40 or carb cleaner is it's flammable, and will act as "fuel" enriching a lean cylinder with the vacuum leak.

It doesn't have to be fancy fuel, as WD40, carb cleaner, flammable brake cleaner (I can't find this anymore?), starting fluid, will all ignite. You can also use an unlit propane torch but it's harder to see it suck in the invisible gas.

You only need a paper clip to get codes from your computer. The CEL should come on with the key on, engine off.
 
I would also suspect EGR after vacuum leaks are sorted out.

But I suspect this is something else as EGR is unlikely to be open at idle. It typically deploys at speed, not while sitting.

If the vehicle starts and runs well it is unlikely to be the TBI.
 
Last edited:
Originally Posted By: eljefino
The idea of spraying WD40 or carb cleaner is it's flammable, and will act as "fuel" enriching a lean cylinder with the vacuum leak.

It doesn't have to be fancy fuel, as WD40, carb cleaner, flammable brake cleaner (I can't find this anymore?), starting fluid, will all ignite. You can also use an unlit propane torch but it's harder to see it suck in the invisible gas.

You only need a paper clip to get codes from your computer. The CEL should come on with the key on, engine off.


well a paper clip and a haynes manual
lol.gif
used to do it alot on my fiero. but it sux counting flashes when you can just have autozone read it for free
 
Clean your throttle body bore and plate really nice. Same for the idle air control valve,
MAnually an visually check all vacuum line s and their connections.
Intake leaks also. You can use propane or spray carb cleane to test for some leaks. The idle will change when you spray a bad area.
 
among other possibles kindly suggested, im still thinking that the heat & expansion from engine at full temp is maybe allowing a gasket leak on the inlet or TBI???...anyone think this is possible?

I wish someone would leave a brand new Ford Transit Connect on the driveway!
 
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