Engine randomly bogs down with Check Engine Light that code reader says waiting for communication?

Tiny
1996TOYTAC2.7
  • MEMBER
  • 1996 TOYOTA TACOMA
  • 2.7L
  • 4 CYL
  • 4WD
  • MANUAL
  • 380,000 MILES
I've never heard of this from anyone before; my truck will idle and run great for a while, then without warning it will bog down when giving it gas (still idles fine even when the bog down is happening). Removed and looked at the ECU. No burn smell or corrosion then put it back. Used electrical contact spray on all the connectors, fuses and relays.

Also, the OBD communication with the code reader works fine except when the bog down is happening. It shows check engine light, and the code reader says it's not receiving code data. Then without any indication the bog down will stop, and the check engine light goes away, and it runs fine. The bog down sometimes can be coaxed into a higher sustained rpm but when the clutch is released and trying to drive it almost stalls out.

Sometimes, when I turn the engine off wait about 45 seconds to restart, it will be fine and sometimes that won't work either. Very random.

I disconnected the battery cables for over 12 hours so the capacitors would drain. Then reconnected them and it starts and runs great until it acts up again and the whole scenario is repeated.

I am really puzzled and frustrated with this. Also, I had a lot of work done to truck lately in a shop that I trust. All of these are new:
IAC
EGR
EGR modulator
PCV valve
Gas cap
Throttle position sensor
Vacuum hoses
Battery
Alternator
Fuel filter
Fuel pump
Throttle de-carbonized
New gas lines
New gas tank flange top

As with any troubleshooting it's speculative. Because there are no codes, but it never had this problem with the old original fuel pump.



Thank you for your help and expertise!
Sunday, September 18th, 2022 AT 7:31 PM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
This sounds like a classic ECM that is going out, I would get a used or rebuilt unit by searching google or eBay. Here is how the ECM is replaced in the images below. Let us know what happens and please upload pictures or videos of the problem.
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Monday, September 19th, 2022 AT 1:30 PM

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