1988 Toyota Pickup Issue with O2 sensor heater circuit &

LARKIMG

MEMBER
1988 TOYOTA PICKUP
4 CYL
2WD
AUTOMATIC
44,000 MILES

22REC engine (Calif), 1-ton

I replaced O2 sensor because I was not getting a good reading then I noticed it appears O2 sensor heater is not being activated. HT pin on ECU is used to ground heater circuit, but is staying high. If I manually ground this pin I get about 1amp, which seems right.

Q: Should this heater be turned on as soon as engine starts, or are there other conditions that gate it? Is this a burned out ECU?

When warm idles poorly, almosts stalls when put into gear. Failed smog due to high HC. Power seems low. Smooth acceleration, but not very quick. Revs up high eventually fine. Freeway speed is no problem. Starts fine.

Added an air leak and that made it worse, so it seems like it is running lean. Haven't found air or exhaust leak. Idle speed air bypass screw is turned out almost all the way to get idle when warm.

3 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi larkimg,

Thank you for the donation.

The O2 heater circuit is turned on as soon as the engine is started.

The idle adjust screw being turned out almost fully indicates the passage is clogges and rrequires cleaning. Get the throttle body cleaned and retest if it runs well.

Have you tried to retrieve for troube codes?
Was the Mass Air Flow Sensor tested?