Anonymous asked in Cars & TransportationCar MakesChevrolet · 8 years ago

Tbi code 22 and 21 at the same time?

Tbi code 21 and 22 at the same time

I have an 88 c1500 chevy with the 4.3l tbi. It has been excellent to me until recently.

It started with random high idles. It wasnt constant. Every now and then id be at a light or something and it would suddenly rev up to around 1600-1800rpm. Id take off and notice that my 'shift' light would act funny. It would stay on when i wasnt in gear (its the 5 speed manual) and also stay on with my foot off of the gas while in gear. It didnt throw a code at all.

Then it started throwing a code 21 at idle when it idled to high i checked the tps and it was working perfectly fine, around .48v to 5v or so, if i remember correctly and it was smooth increase and decrease.

It drove fine for a few days.

Then it started idling high much more ofter and stall while driving down the road in gear and i let off the gas. Thats when i got the code 22 as well as the code 21. Its stalling out now in gear whether or not im on the gas and idles high almost frequently. My check engine light goes on and off sporadically. Ive che ked the tps a few times now and still its where it should be.

I have a feeling that its my ecu but i have now way to tell.

Any ideas to what could be causing this?

I rebuilt the throttle body about 3 months ago and replaced the old tps and ia. Along with new injector pod.

Any help is much appreciated.



1 Answer

  • 8 years ago
    Favorite Answer

    Miguel, I'm glad you asked before you replaced a ton more parts, but I wish you would have asked before replacing the TPS and IAC. Money wasted. :(

    TBI trouble code charts from the GM manual are here: Look at the first link towards the end of that post.

    You need to do a good inspection of the engine bay first off. Replace ALL vacuum hoses if they are not already new. Make sure all electrical connections are good, no bare wires, etc. In looking at that code, 21 and 22 are pretty specific in what will set them, I'm thinking either a wiring issue, or a vacuum leak. Vacuum leaks are extremely common at this age of your vehicle. They tend to leak around the throttle body to intake, so verify all the bolts are tight, that no wires got pinched, etc. Test with an unlit propane torch "sprayed" around the intake. If idle picks up, you have found a leak. Also check the intake manifold to head bolts, for some reason they can loosen up as well. Just make sure they aren't super loose.

    Additionally, if you rebuilt the throttle body, did you mess with the idle stop screw? If so (and even just due to the throttle body rebuild/IAC replacement) you need to google "tbi minimum air adjustment" to make sure the IAC is set properly. Since both TPS codes will set based on vacuum, IAC *can* play into this.

    Do not pay attention to ANYONE who tells you to randomly replace parts. Also, the ECM on these vehicles is incredibly robust, IF they fail it is very rare. That should ALWAYS be your LAST item to consider for replacement. Always use the GM manual for troubleshooting first, but remember, that doesn't cover EVERYTHING, like bad pin connections at connectors, corrosion on connectors, etc.

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