Javelin
Javelin MegaDork
2/24/15 11:32 p.m.

Trevor's Honda has everyone at their wit's end. It's an 89 Civic LX sedan with the D15A1 1.5L SOHC 16V TBI motor. 200K miles, auto, A/C. It has new rings, rod bearings, and a rebuilt head. It basically ran like crap (and a shop did the rings).

The TPS is coding as bad, but when I back-probed it today with a multi-meter, it showed 0.91V at idle. I adjusted it to 0.50V at idle and it runs much better. In gear, foot on the brake it idles rock solid at 1100 RPM with the A/C on or off. In Park or Neutral the idle hunts from 1400 to 1900.

WHat should I look at next? Base timing, IAC, or??? It has a brand new distributor (complete unit), and all new wear items (plug, witres, rotor/cap, PCV, oil & filter, air filter, etc). Everything is stone-ass stock.

mndsm
mndsm MegaDork
2/24/15 11:36 p.m.

Iac.... I.don't know much about Hondas, but my DSM ate these things like candy and did just that.

turboswede
turboswede MegaDork
2/25/15 12:14 a.m.

Yup IAC or vacuum leak.

Might look at making sure the passages in the TB are clean while you're in there.

edizzle89
edizzle89 Reader
2/25/15 6:11 a.m.

if i remember right some of the ~90's hondas had common issues with idle surging. another thing to check besides the IAC is make sure the cooling system is purged and has no air pockets in it and is completely fully. the coolant temp sensors dont like seeing the temp change from air to water and it makes the idle jump around

Kenny_McCormic
Kenny_McCormic PowerDork
2/25/15 12:11 p.m.

Play the "unplug stuff until it starts running better" game?

tpwalsh
tpwalsh HalfDork
2/25/15 2:12 p.m.
edizzle89 wrote: if i remember right some of the ~90's hondas had common issues with idle surging. another thing to check besides the IAC is make sure the cooling system is purged and has no air pockets in it and is completely fully. the coolant temp sensors dont like seeing the temp change from air to water and it makes the idle jump around

This. I have a dual point engine that was doing this due to an air bubble in the idle control valve. Also of a note, the throttle cable was slightly tight, which also resulted in this behavior. Was a little maddening to be honest.

old_
old_ Reader
2/25/15 4:41 p.m.

Clean out the IACV. Very common for them to get clogged with carbon. Very easy to do on that car.

Streetwiseguy
Streetwiseguy PowerDork
2/25/15 9:03 p.m.

Make sure its got hot water running through everything that should have hot water in it. Four things control idle- Base throttle opening, idle air motor, air conditioner idle-up mechanism, and a cold idle wax pellet doodad. Almost all Hondas of that vintage, when they have an idle issue, have the issue you are dealing with. Almost all of them are fixed by repairing the cold idle system, which either has a blocked or missing coolant hose, or a seized mechanism.

Or it could be something else.

Javelin
Javelin MegaDork
2/25/15 11:42 p.m.

Thanks for all the tips! Bossman said not to touch the car, so he can figure out how to clean and bleed the IACV. At least I got it to start and run.

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