98 Tacoma 2.7 runs a bit sluggish - any suggestions?

I have been working on reviving a 98 Tacoma 2.7L that sat for 9 years. Its been a process to clear the CEL and get it to run smooth and I still have some weird hesitations during acceleration as well as the idle dipping. The idle runs about 800, but will dip to about 400 sometimes lower and choke for a few seconds before picking back up.
There is no CEL coming on at this time. and I have swapped or replaced quite a bit in the process. Plugs, wires, Throttle body, coils, Injectors, Fuel pressure valve, fuel filter, EGR valve, PCV valve.
I have had a mechanic check it out and they suggested I swap the ECU as they could not find a reason for the problem. I got a replacement and swapped it out. The problem returned as the ECU went through the learning process.

Any other thoughts as to what would cause brief hesitations during acceleration and idle dipping would be appreciated.
There is no exhaust leaks or vacuum leaks detected when checked.

 

Welcome to TW...It sat for 9 Years?.you cleaned the fuel tank out?

 

Did not drop the tank.

 

If you’re having issues with the idle id check the throttle body and related components. Probably needs a good check and clean. TPS, IAC etc

 

Throttle body is replaced with one that was rebuilt. All sensors show proper connections and no CEL indicating a problem there. The old throttle body was not closing properly even after a good cleaning.

 

Take the catalytic convertor off/down and see if you can see through it.

 

Cat has been replaced, as the old one was rusted at the joint and caused an exhaust leak.

 

What was mentioned above about the 9 year old gas, that has turned to varnish. Prolly has moisture in it as well.
Drain it, and refill it with fresh. Add some Seafoam to the tank and take it for a drive. I wouldn't run gas that old thru a lawn mower.

 

pumped out old gas, and have ran 3 tanks with seafoam. Although there have been some improvements with the way it runs, it still has this odd behavior. I get occasional backfires as well. (I began this project last October)

 

Running out of ideas... there is a post in this Forum titled IAS/TPC advice, this might give you some direction

 

I'll look into it, thanks!

 

All these Parts you Replaced OEM or Aftermarket?

 

Some are aftermarket, as getting oem can be difficult. Specific item you are curious about?

 

new injectors without servicing the fuel tank after it sat that long wasn't the best choice. another easy thing to check off is just to clean the MAF sensor most likely not the root of the problem but gotta narrow down the easy stuff first

 

we've also seen a lot of clogged oil pick up screens, but thats more the cause of low oil pressure and low idle and you have other things going on

 

Fuel filter was changed out, and fuel pressure tests within spec, although not sure of a way to monitor if the pressure changes when driving. MAF is brand new from Toyota.

 

you said your CEL was on and those codes are currently a secret to us. Look for something related to TPS, IAC like others have said, these things send codes. Your idle is constantly fluctuating so something is causing the dip and your ecu is saying "hey engine, adjust this so we can stay running." My engine would get stuck at high idle for a few seconds after coming to a stop, I had TPS CEL codes that were intermittent. I cleared it and it didn't come back for a while. I did a tune up and cleared it again and it has not come back for a very long time.

 

Was the air filter/housing/intake tube inspected? 9 years sitting, I wonder if a mouse made a home in there somewhere.

 

Air intake is clean, and there is no CEL currently. I worked through the codes I was getting and when I finally got all the codes cleared this is where I am at. It idles off a bit, not sure how to describe it. I get 1/4 sec hesitations mid acceleration.
Example: take off from a stop about halfway through 1st it hesitates before resuming, and again on second, if it happens in 3rd it's hard to notice.
Otherwise the truck does a great job of running.

 

Drop outs like that are usually indicative of a throttle position sensor (TPS), but not always. Did you transfer your old TPS to the new throttle body? Does your truck have EGR?