Idle Problem on 2.7 CIS engine

[LCOX]

I'm sure this problem has been covered before on this forum.

I have an idle problem on my 2.7 cis engine. Engine cranks and runs fine cold and hot.

The problem is the idle speed lopes up and down with the tach hand loping up and down as well. This is not a similar problem where the tach hand swings wildly regardless of speed. The idle speed here lopes up and down.

I have the idle speed screw turned out 6 full turns to help the problem some. If it is turned in several turns the car will stall. I've also adjusted the fuel/air mixture screw down in the sensor plate housing more rich and more lean as well with no sucess.

Could this be a warped airbox. Is this car too rich or lean. Thanx. L

[redstrosekNic]

Don't make blind adjustments! I would get a measurement of the CO to be sure of the idle mixture. Gunson gastester is a great tool if used correctly. If the idle is hunting, the mixture could be rich. I would get a CO reading before assuming rich/ lean.

Perhaps the cold start injector is leaking, causing a proper mixture when cold, but too rich when warm.

Good luck!

[redstrosekNic]

Gunson Portable Gas Tester Analyzer

[Targalid]

The fluctuating idle is usually a symptom of a too rich mixture. Before you fiddle too much with the mixture I would rule out air leaks. Is anything changed from before when it was running well? You do not list your location so you may or may not be violating some draconian laws if you adjust the mixture screw without proper dispensation. Calling911 has a simple procedure on this forum for adjusting CIS without gauges that worked well for me.

How to setup CIS with no gauges

My personal advice is to run a can of injector cleaner through the fuel system before changing anything. Costco has a good deal on Techron by the sixpack. They also have beer by the case.

[47silver]

1. check all vacuum lines.
2. check the pop off valve o-ring and how it is sealed.
3.. check hose going to oil tank.
4. check hose going to distributor.
5. if you have power brakes check that hose
6. if you have cruise control check those hoses.
7. a dirty fuel filter might not be good for the idle.
8.. i would also check the points.


from what i know that if your engine surges at idle it could be:
1. leaking vacuum lines
2. worn air flow sensor and (not a good thing).

[stlrj]

Originally Posted by LCOX

I'm sure this problem has been covered before on this forum.

I have an idle problem on my 2.7 cis engine. Engine cranks and runs fine cold and hot.

The problem is the idle speed lopes up and down with the tach hand loping up and down as well. This is not a similar problem where the tach hand swings wildly regardless of speed. The idle speed here lopes up and down.

I have the idle speed screw turned out 6 full turns to help the problem some. If it is turned in several turns the car will stall. I've also adjusted the fuel/air mixture screw down in the sensor plate housing more rich and more lean as well with no sucess.

Could this be a warped airbox. Is this car too rich or lean. Thanx. L

Definitely too rich! You forgot to mention how the smelly the exhaust smells, right? You'll need the "T" allen CIS tool to lean it out to make it run right.

[T77911S]

well you have already screwed with the mixture so now class is in session, and by that i mean you can now start "playing: with things and learn more about your car.

but, before you do anything else, you need to first make sure the ignition is in top condition: new plugs, rotor and cap, make sure the timing is set properly and the advance is working and you need to make sure you have no air leaks. a smoke test is the best way to check that.
all of this needs to be down because it all effects mixture.

now you need to check fuel pressures. you need to check system pressure, cold control pressure (CCP) and warm control pressure(WCP). if those are not is spec, that needs to be resolved.

once all that is done, NOW you can go back to mixure adjustments.
you dont need a special tool to do this. the long 3mm allen from one of those craftsman sets work perfectly.
right or CW makes it richer. R= rich. CCW = leaner.
there are several ways you can do this. once the engine is running, you can reach in and raise or lower the sensor plate to figure out if the mixture needs to be richer or leaner. i only do this if the car wont start and suspect the mixture is way off. to me this is more work, although it will tell you if it is rich or lean.
you can also adjust the mixture rich until the rpm's drop and then lean until they drop and then set it in the middle, or i usually start with it more to the rich side of middle. then i blip the throttle and if the RPM's drop below idle then come back up, it is too rich. so i lean it out a tad and repeat.
in the end, set it so the RPM's have just a very very slight dip when returning to idle or no dip at all. but want it right on the edge of trying to dip down when you let off the gas.

after you have done all this, you can still go have the mixture checked with an analyzer just for peace of mind. even though i have an LM2, i have found that this puts it right where it needs to be so i dont even get it out anymore. right now my RPM's drop staight to 900 and stay there. no dips, no surging and my decel valve is removed so the RPM's drop quick. (it was removed becuase the RPM's where hanging and not coming down).

[LCOX]

Thanx for all the info

I'll get started checking things out.

[kach22i]

After you change out all the vac lines there will still be the intake manifold hoses near the air box and throttle body, plus a hose on the back of the engine, passenger side, each which require a partial engine drop to get to.

In the 101 Projects book page 96, #3 caption shows a good picture and explanation of this intake manifold hose trouble spot.

I experience the same issues you do, found my two remaining leaks using the starting fluid method.

I have a few tricks on living with this condition until you can get to fixing the car.

1. Start the car and run for about five minutes to warm up the engine a bit.

2. Wait about five or ten minutes to allow the heat to expand and seal the leaky connections.

3. Re-start car and drive off, the bobbing tack and engine variation of idle should go away along with any possible stalling issues you were having.

[pgapro2002]

Just replaced my coil & coil wire. Started it and sounded like everything was running good, no more missing/cutting out. Drove a mile down the road and it started blubbering, and almost died. Had to keep my foot on the gas pedal to keep the revs up at about 1000.....anything under that it would blubber and almost die. Adjusted the mixture with the 3mm wrench, got it to idle at 1000 and it seems to run ok. Is 1000 a good idle point? Thanks in advance.

[pgapro2002]

Forgot to mention in my earlier post..............when I changed the coil, I did not change plugs, rotor cap, distributor cap. Car was running great before, but kept dying out due to what I could determine was bad spark, faulty coil and/or coil wire. Maybe I am wrong??

[Paulporsche]

As redstroseNic said, you should get your fuel and control pressures, and your mixture measured. In order to get a good idle speed (when warm) which should be about 900, you need to use both the mixture and air bypass screws. You should set the CO% first then use the bypass screw to set the idle.

Offhand, it sounds like your mixture is too rich. A hunting idle is a common symptom of this. It's possible someone set the mixture too high to mask the spark related other issues you had.

Getting the cps measured and the mixture set to about 3.5% will give you a good baseline, and may set everything right.

As a general rule you should always make sure your ignition components are in good order before you do any fuel injection investigation. Check and set your points, rotor, cap, and plugs if they haven't been changed in a long time, or if you don't know when they were installed. The factory wires on these cars last a long time, but not forever!

Finally, as someone mentioned, make sure there are no vacuum leaks. The hoses get old and brittle and eventually leak. You can also get leaks @ the AAR, AAV, decel valve, plugs, and gaskets.