slight miss at idle

[Blacktop81]

i have a 1987 Mustang LX Coupe factory 302 with speed density no mods. it has a slight miss at idle thru 2000 rpms sometimes it will pop thru the intake if i try to quickly accelerate it. Also the car seems to run hot well according to factory gauge im running a 180 thermostat. Today i did a compression test and all cylinder check out good (150-160 psi) but i notice the spark plugs were white so i take its running lean. What causes a lean condition? Also timing is set at 10 degrees w/ spout disconnected.

 

[HISSIN50]

Pull codes and run a cylinder balance test after getting KOER codes.

Good luck.

 

[jrichker]

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[Blacktop81]

Will pull codes and do balance test today lets see what I come out with.

 

[Blacktop81]

Ok, I just finished pulling some codes:

KOEO:
81- Thermactor Air Circuit
82- Thermactor Air Circuit, Integrated controller circuit
84- EGR Control Circuit
85- Canister Purge Circuit

KOER:
12- Idle speed control out of specified range
94- Secondary air system inoperative
44- Air Management system inoperative
33- Canister or EGR valve not operating properly

Cylinder Balance came out fine

I did find that the a/c vacuum line was broken so I fix that. I also connected a Vacuum gauge from my previous car and it read 18 in @ idle.

I had removed all the emission stuff and removed the egr valve but I had made a chip for it but I guess it didn't work. Would it make it lean out that bad?

 

[jrichker]

Ok, I just finished pulling some codes:

KOEO:
81- Thermactor Air Circuit
82- Thermactor Air Circuit, Integrated controller circuit
84- EGR Control Circuit
85- Canister Purge Circuit

KOER:
12- Idle speed control out of specified range
94- Secondary air system inoperative
44- Air Management system inoperative
33- Canister or EGR valve not operating properly

Cylinder Balance came out fine

I did find that the a/c vacuum line was broken so I fix that. I also connected a Vacuum gauge from my previous car and it read 18 in @ idle.

I had removed all the emission stuff and removed the egr valve but I had made a chip for it but I guess it didn't work. Would it make it lean out that bad?

Removing the emission control hardware does not make these cars faster. All it does is make the computer angry, spit codes and may even make it run in limp mode with reduced performance and economy. All of the emission control equipment shuts off the instant the computer sees WOT (Wide Open Throttle). If you still have the catalytic converter H pipe, the cats will clog and fail without the extra air provided by the smog pump.

 

[Blacktop81]

Removing the emission control hardware does not make these cars faster. All it does is make the computer angry, spit codes and may even make it run in limp mode with reduced performance and economy. All of the emission control equipment shuts off the instant the computer sees WOT (Wide Open Throttle). If you still have the catalytic converter H pipe, the cats will clog and fail without the extra air provided by the smog pump.

i had removed the emission hardware to clean up the engine compartment and the car has an off-road h-pipe. The car had a slight miss since i bought it when it had all emission stuff and egr.

 

[Blacktop81]

i fixed code 12 by cleaning out the idle control valve. Hooked up the DVM set to ohms to each spark plug wire and the distributor cap on found on bad wire. So i replaced the cap and wires and it made a difference but it still has a miss around 1200-1500 rpms. So tomorrow im going install the egr valve and solenoid bac on.

 

[DSGB347]

In the past with my 89 musntang GT I 've have missing caused by a bad plug wire once. This also caused my to have a little backfire throug the intake. as for the running lean have you checked your fuel pressure. I've had a pressure regulator go slowly and it caused hard starting and lean white to show on the plugs. If its a bad regulator I recomend adjustable one. When I was fuel injected i used a Kirban worked great with my Walbro fuel pump.

 

[strtrcr50]

Removing the emission control hardware does not make these cars faster. All it does is make the computer angry, spit codes and may even make it run in limp mode with reduced performance and economy. All of the emission control equipment shuts off the instant the computer sees WOT (Wide Open Throttle). If you still have the catalytic converter H pipe, the cats will clog and fail without the extra air provided by the smog pump.

That being said, I have read that the smog pump is to provide more air for the second set of cats so they can continue combustion. In the case of most with aftermarket cats(1 pair instead of 2), is it still as necessary to continue with the smog pump? I ask because in my case, I have gone to an exhaust consisting of shorties(bbk), an xpipe with 2 cats(pypes), and a catback(pypes). When I allow my smog pump to run, when cold I get backfires through the pipes on medium to hard acceleration. Goes away when all the way warmed up. When I disable the thermactor through my tweecer, I never get any of the same backfires/popping. Also, when I don't have the smog pump disabled in the tune, I can tell because I get a different exhaust note while cold.