Technical Tips > Post 84
1986 C4 MAF Sensor replacement?
peterw:
Thanks for the info.
I will contact Chevparts about the manual.
peterw:
Once I got out and driving again the car seemed to come good. Maybe the computer had to learn again after I reset it.
No MAF code and car seemed to run a lot better, wouldn't idle when cold though.
Symptoms and research told me it was likely Idle Air Control valve though I didn't get a code pop up.
I have replaced the IAC and now car starts properly, idles when cold and seems 100%.
Car has only done 50,000 miles in 34 years so these kind of gremlins don't surprise me.
Thanks to you guys and youtube I am back on the road.
Pete
sirfixalot:
My 87 is now starting but rolls over like it has a big cam am suspecting the idle control valve or the wiring connections the schematic shows 2 coils so I am tipping if there is a high resistance connection in plug or wiring it could upset the balance operation of the valve. I found a test M/F test plug to check voltages but was $90 US plus post so will do some looking tomorrow. My car also had a 33 code which i cleaned and checked all connections and code dissapeared.
peterw:
The faulty IAC symptoms were - no idle when cold and warm idle was 1100 and sometimes hunted. Otherwise the car went well. My googling told me this was typical of IAC problem.
You will need to take the throttle body off to get to the IAC. It looks accessible but they didn't allow any room to put a spanner on it. I tried to make a spanner for it but failed.
When I was pulling it apart one of the plastic vacuum tubes broke. I tried bending a few of them and they were very brittle.
I replaced them all with rubber vacuum line (4mm) and just required a couple of bits of plastic tube to adapt to existing fittings.
It is possible that a broken vacuum tube was to partly to blame for the idle problem but the IAC was very grungy up so I was happy to have changed it.
It's not hard to change out the vacuum hoses once the throttle body is off.
You will need a gasket for the throttle body, I couldn't find one in Australia so I made one. It's time consuming making gaskets from 1.6mm gasket sheet so if you are ordering from USA you might get one of them thrown in. Cost about $US10-15 for a complete kit.
I ordered my IAC from Summit Racing on a Tuesday and it arrived on the Friday. Amazing.
sirfixalot:
Checked the voltages on the 2 coils in IAC had 9.13V on green pair & 0.9V on blue pair with ignition on, engine not running.Also thru tested wiring direct from computer to check for continuity, coils on IAC both test at about 56 ohms. Removed vacuum pipes from rear of manifold & connected to vacuum pump both held good vacuum so no vacuum leaks in hoses & valves,Fuel regulator. Starting to run out of ideas.
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