OK i will start at the start, i did a service on my carbed 305, new plugs, leads, cap, rotor, coil ect after which when i started it from cold i would notice a very slight missfire which cleared quickly. i just put it down to the damp english weather. after a few weeks of this minor temporary missfire i didnt use the car for 2 weeks and when i came back to it it started fine with choke like always, after warming up a little on choke i gave it a rev to disengage the choke like i always do and it began to idle badly at around 400 and miss.

I put this down to the new plugs so i changed them back to the previous known working plugs but to no avail, likewise with the leads, then i came to the coil and found that the earth wire had shorted out and melted the wire and burnt the coil a little, i thought this was the issue and changed back to the old know working one but still have the same issue

I have checked the CTS which is good and new O2 sensor is reading .30v as the manual suggests i checked for air leaks with a scope and brake cleaner to no avail, the MAP reads around 3.20v at rough idle and goes up to around 4.50v when revved

• Could the problem i had with the coil have damaged something else electrical somewhere?

• Does anyone know what i looking for reading wise from the TPS?

• Strangely when idling at around 400, if i put it into gear the revs do not change like you would expect, normally shifting into gear would drop the revs by a few hundred.

• When rough idling , if i touch the gas a little to bring the revs up, by the 1000 mark the missfire clears and its running smooth.

• Sometimes when i start it it will idle ok untill i give it a little rev at which point it drops back to the rough idle

• The car still drives ok untill i release the gas at which point the revs drop back to rough idle.

• If i unplug the ecm the idle seems to clear and raise to normal which would suggest to me that a sensor or something is lying to the ECM making it change the fueling or timing.

If anyone can chuck some ideas at me of what to try i would greatly appreciate it as i haven't driven it in over 7 weeks and im going out of my mind

 

A low speed misfire can come from many things.
Bad gas, carb too lean, carb to rich. Plug wire on manifold.
a 7 cylinder feels like a 8 cylinder over 1500 RPM.
You can use the old method of pulling one wire off at the plug side and watching idle change and replacing the wire back on the when the difference is noted. Do this one at a time. Also - plug wires order is 1,8,4,3,6,5,7,2. I would put your idle in drive at about 550-600 anyway. Check your power brave booster valve.

 

quick update, its still the same, i just got done checking the compressions and they all seem good between 170psi and 179psi, apart from one which read 185 psi, which im assuming is a worn valve guide letting in a little oil which would explain the puff of blue smoke after its sat for abit.

new fuel filter fitted,
TPS read .50v and climbs smooth when the throttle is opened,
the MAP reads about 3.2v at rough idle which i think may be abit high i dont know, it reads 4.5 when revved,
o2 sensor reads .50v on idle .75 when revved
disconnecting the EST makes the revs jump up a few hundred and smooth out
likewise if you disconnect the ECM


well thats about all for now, i think i should try changing the junk inside the dizzy, could the fault with the coils earth have damaged something

 

I'm going through a similar issue, I just tuned up my ignition system and my car has been missing under load and idling a bit rough. I actually ran across something in the troubleshooting section about the EST system changing the timing and idle when the car is placed in gear. If I remember right, you can ground the test port on the obd1 connector with a paper clip and the car should idle down if the EST system is working correctly. I believe it's the second port from the right in the top row on the obd thing... takes literally 3 seconds with the engine running so you might give that a try.

 

Nevermind, just read your second post which seems to indicate that the est system is working okay. You can try checking the pickup coil in the distributor by connecting an ohmmeter to the pickup coil leads. Testing between the lead and the distributor housing should result in a reading of infinity and testing between the two leada should result in a value between 500 and 1500 ohms.