Last post on Aug 22, 2012 at 10:55 AM
You are in the Chevrolet Metro/Geo Metro
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Geo Metro, Chevrolet Metro, Hatchback
#1349 of 1864 Re: 95 geo 1.0 rough idle + loss of gas milage [zaken1]
Jul 11, 2008 (1:43 pm)
Mljwire here; (Les)
I have done your suggested testing on the rough idle and loss of gas mileage on my 95 Geo. I am not sure about the issues I found with the TPS and I now believe the rough idle is actual slow idle as described in the idle air valve check.
1995 Geo Metro
Manual 5 speed
Manufactured in Canada.
Complies to US.
Throttle Body 13400 50G11
1. Throttle position sensor. (Denso 13420-50G00, 198500 3090) It is adjustable. When checking I do not see the switching terminals as you mentioned and as the diagram and set up procedure shows in the Haynes Repair Manual for 1985 to 2001. I marked the TPS position and removed it and rechecked it by rotating the coupling fully CW & CCW. I do not see the switch. I do see the resistor and the wiper. The feller gauge between the stop-screw could not be set. I went to Advanced Auto and compared a new TPS of the same manufacture and part# and it tested exactly the same. I have included the resistance readings of the TPS. Please let me know if I am doing something wrong.
Pins CCW CW
1-2 Inf. Inf.
1-3 .004ohm 3.31ohm
1-4 3.65ohm 3.65ohm
2-3 Inf. Inf.
2-4 Iinf. Inf.
3-4 3.67ohm .49ohm
2. Spark Plugs. New in 2007. I started with Champion RN12YC. I checked the Champion website and confirms the correct application. The plugs are nice and tan, no carbon or oil and gap measured good. I changed them to Autolite AP63 and set the gap to .041”.
3. Cap and Rotor. New in 2007. I inspected the cap and rotor and found no carbon tracking. I cleaned the slight oxidation on the conductor pins in the cap. The leading edge of the rotor looks like new. I noticed what looks to be hairline cracks in the top of the cap plastic at the point where the three conductor pins mount. The cracks migrating toward the rotor contactor. I was going to replace it but when I inspected the cap from Advanced Auto I noticed the exact same condition. I plan to get a different brand.
4. MAP Sensor. I checked the electrical connections for corrosion and did not see any. I checked the electrical connector for bad wires/connections, ok. I replaced the vacuum line to the TB and checked the conection spigot, ok. I checked the voltage of the MAP sensor and from the
OBK to GBK wires
The voltage measured 3.66v with the key on and not running.
Reeve engine 1.6v
5. Idle Air control Valve. The Haynes manual say the idle air control valve is pre 94 models. I have a 95 which has idle speed control motor I tested the motor by placing 6v on the ISC motor terminals and the motor extended and retracted. I do not see the ISC motor on the wiring diagram. I found an idle up from the A/C control amplifier on the heating and A/C diagram but I have not located the module yet. There is also a 15a IG fuse that I also did not locate. I checked all the 15a fuses under the dash, they are ok. Under the passenger side dash there are two boxes a metal case which I believe is the ECM and a black plastic box, is this the PCM?
I believe this could be a good possibility because I noticed that the idle speed does not change when I turn the A/C on and off or when I step on the brake. At this point I believe that my rough idle may actual be low RPM. I tried to do a check of the RPM but it is rudimentary at best as I used my old tach/dwell meter set on 4cyl and calculating about ¾ of the value which I am sure is inaccurate but I was hoping it would be close.
RPM (0.75 of actual reading on 4cyl tach)
Hot 350rpm sounds extremely slow and it looks slow.
6. Dirty Fuel. Changed fuel filter annually. Changed it again. The rough idle seems to have started a 1 ½ years ago progressively getting worse. I have used the Techroline cleaner.
7. EGR Valve. I removed and cleaned the EGR valve again. It was still pretty clean. I checked all diaphragms and vacuum lines for leaks and operation. Last time I went through and did all of the operational checks in the manual. This time I confirmed that the diaphragm was moving when revving the engine.
8. Timing. I have owned this car since 3K miles and have never adjusted the timing. The timing is specified under the hood as 5deg at idle.850rpm. I checked it by jumping the test terminal as specified and it is at 5deg BTDC at idle although the manual says to check it at various RPM I do not have the correct tach so this check is also rudimentary but at idle it is correct.
9. PVC valve. Replaced.
Changed the air cleaner.
Checked and repaired all vacuum lines.
Replaced Timing belt.
Sorry about the length. I want you to have details. I am thinking I need to figure out this idle speed control motor control circuit because that is supposed to increase the idle with the A/C on and I believe it used to increase when the brake was depressed. The idle does not increase for any conditions that I see.
#1350 of 1864 Re: 95 geo 1.0 rough idle + loss of gas milage [mljwire]
Jul 11, 2008 (8:30 pm)
Thanks for all the detail. It was very helpful. But I'll be brief here, for simplicity's sake.
1> It sounds like either TPS pins 1-3, or 3-4 are the ones that switch. I'd use whichever pair's reading changes abruptly between the low and high figures when the throttle is opened a little above idle, with the housing set about midway in its travel. Then lock the housing in the position where the switching takes place when the throttle linkage opens .018" from fully closed throttle.
2> I'd stay with the Autolite plugs, as you have them set, and would definitely search around for a distributor cap without manufacturing cracks (try a NAPA parts store).
3> It sounds like the idle air control circuit is not working. I suppose it may just require more extreme conditions to activate it; but I expect it is inoperative. I can't help you with the repair procedure, but there should be an explanation in a 1995 Mitchell electrical systems manual (a huge, thick book that covers all brands of cars). The trick is to find one. Local library reference desk would be a start. A good fuel injection repair specialist will probably also have one, but may or may not cooperate with your need for information.
4> I wouldn't try this until all of the above items are resolved, (PARTICULARLY THE IDLE SPEED CONTROL MECHANISM) but sometimes the idle air bypass screw in the throttle body has to be reset. This cross head brass screw is hidden inside a boss, on the driver's side of the throttle body, near the rear edge of the casting, perhaps halfway up between the throttle body mounting flange and the air filter housing. There is a black rubber plug covering the screw when they are new. Turning the screw in (clockwise) enriches the mixture, and usually slows down the idle. Loosening the screw leans the mixture and speeds up the idle. There will be a range of adjustment over which the idle quality is pretty good, and there should be a sharp peak of smoothness within that range. But the throttle position must be set right before you can find that spot, and that means either fixing the idle speed control, or resetting the throttle stop to a further open position.
5> I assume you've checked the compression pressure. It should be very close to 195psi (which is a lot more than it is on most cars). Anything less than 180 fails.
Everything else you mentioned sounds good.
#1351 of 1864 Re: '95 with overly rich mixture [zaken1]
Jul 12, 2008 (9:08 am)
If you have not fixed problem try Helm Manuals. You can get specific ones for mechanical,electrical,body. They are very detailed step by step manuals.
#1352 of 1864 Re: 95 geo 1.0 rough idle + loss of gas milage [zaken1]
Jul 12, 2008 (9:16 am)
Thank you for you time. I am working on getting a factory manual and I will try your suggestion.
#1353 of 1864 Re: '95 with overly rich mixture [robthom2001]
Jul 12, 2008 (9:18 am)
Thanks I will look for them.
#1354 of 1864 Will not start
Jul 13, 2008 (5:44 pm)
1996 Geo Metro only fires one time on each try.
Engine will fire one time each time the key is cycled. Will do it as long as I want to keep trying. If you continue to hold the key in the start position after it has fired it will not fire again until key is recyled. I have checked wiring harness plugs in the engine compartment. Checked crank sensor,installed known good distributor, coil, ignitor,computor. Engine was changed in this car by previous owner. I bought it not running. What am I missing?
The engine is cranking over normally. It fires the number three cyl one time only each time the ign key is cycled from off to start/run. Also this is a 1.0 3 cyl. 5 speed. The timing belt has been checked and it is timed correctly.
Jul 13, 2008 (7:21 pm)
Only one cylinder fires...
Ignition fuse 20 A? not likely
Ignition switch? more likely
imho of course...
#1356 of 1864 Re: Will not start [dano84]
Jul 13, 2008 (7:58 pm)
Here are the possibilities that occur to me:
1> Cracks or carbon tracking in distributor cap or rotor. (Try checking for spark directly from coil, instead of from distributor cap)
2> Firing order of plug wires in cap incorrect.
3> Misaligned or defective ignition pick up unit or air gap between reluctor and pick up not set correctly.
4> Computer or igniter intended for car with automatic transmission, or for wrong year model.
#1357 of 1864 Re: '95 with overly rich mixture [chevelle67]
Jul 14, 2008 (7:35 am)
I want to thank all who helped me, especially senormechanico for the diagram, when you don't have any stickers under the hood, its a pain to find info thats not in any of the manuals. You guys are great! Keep up the good work. Thanks Again, Chevelle67
Jul 17, 2008 (4:52 pm)
Having checked all the sensors (all were ok) I finally was able to lean out the mixture by adjusting the throttle position sensor in the counterclockwise direction.
I marked the original position, and backed it up a little bit. I drove it a couple of miles to see how it acted. At first, the idle speed was quite high, but it corrected itself after a mile or so. After repeating the above procedure two times, I tried it all the way counterclockwise just to see what it would do. After the engine heated up to normal, the idle went into a hunting mode, speeding up and returning to normal. I then readjusted it clockwise just slightly to the point where the hunting ceased. I now have a peppy car with a CLEAN exhaust pipe! Thanks to everyone for suggestions, especially to Joel (zaken1)