Hello folks, my 94 4runner just ticked 187k when the knock sensor went out in addition to an issue with the distributor. I couldn't afford to have a mechanic do the labor, so I bought the parts and started researching. Was more technical work than I have done mechanically, so I talked through the finer details with a mechanic friend. He had done some work on it in the past and recommended I do a few other things while I was working on it. I just got it back up and running but I can't quite track down what may be causing the lag in acceleration. I'd love any pointers on diagnosing the issue...I'm a baker and we always say to never adjust more than one part of a recipe at a time so you always know the impact of a change. The work on the 4runner has left me unsure where to look next.

Work completed:
Knock Sensor+wire harness
Both valve cover gaskets (driver's side took some serious persuasion to coax free thanks to some significant silicone sealant)
Intake manifold gaskets + plenum gasket
Timing belt component kit (including the water pump, thermostat, idle pulley, tensioner pulley + tensioner)
- timing marks lined up on camshafts after 2 full revolutions
New distributor
- new coolant and bled the radiator (thermostat was stubborn to get to open up, but fine now)
- timing set at 10 degrees before TDC with jumper on the correct ports on the diag panel while the engine was warm

The timing took a few attempts since the rotor I bought didn't seem to have a marking. After some guess work and the timing light. I thought it was warmed up fine, but found out the thermostat had a stubborn bubble. Once it finally opened up and burped the timing adjustment made the idle much more like before.

The issue:

• lagging acceleration occasionally, but tends to crop up at 3500 rpm...and very likely when on slight inclines and seems to happen more frequently when warmed up
• a cold start seems to stutter right at the start, idles for a few seconds at 500 rpm before slowly climbing up to 800
• drives fine initially, then about 20-25 minutes in I notice some lagging
• TVV sensor got some Macguivering by the previous owner. It fell apart when I took the intake manifold off and it was not salvageable. I bought a new sensor but have yet to install it, mainly because I don't want to pull the intake off again.

It is driveable, but I have to drive much more mindfully. Today on the slightest of inclines I couldn't get it above 65 and it wouldn't climb past 3500 rpm. One the slightest of downhills I was driving 70. It used to lag slightly when I had a new muffler put on but this is a drastic difference. I rechecked timing, used a hose to try and hear any leaks but heard nothing that screams that would be the issue. Is this an airflow sensor, fuel pump issue??? Or is it related to something in the work done recently? I was thinking I have a gasket leak but haven't been able to confirm it.

Any places I should start to diagnose what is causing this? My wife and I have a 7-month-old, just bought a house and paid to put in a new AC...so, I'd love to keep it running for a year or two longer...

Other details that may or may not be important: My first drive out of the neighborhood, I noticed some significant lag in acceleration around 2500 rpm. Just no response even when I floored it...just a slooowww climb on the accelerator. When I got back home that evening, I went back with the timing light. Shorted the ports like before and confirmed the check engine light was flashing (sporadically) and it was at ~9-8 degrees. I made a slight adjustment back to 10 degrees. Today, I drove it on the same route and it seemed much better...until it wasn't.

 

Do you know what the timing was before you pulled it apart? Factory is 10, but these engines really like 13-14 advance.

Other good things to check are the TPS and AFM to make sure they are in spec, as well as making sure there arnt any air leaks after the AFM.

any check engine codes currently? even if the light isnt on, there may be codes stored.

 

Rattle, thanks for the reply!

I wish I would have thought to take a look at it, but I failed to even think about that. I did just adjust closer to 14 degrees and it seems to accelerate like its old self for now up to a point. Consistent highway speeds still seem to be a stretch goal at the current state.

I will take a look at the steps to diagnose an issue with the TPS or the AFM and see if that helps the top-end speed. I'll drop by a shop and see if I can get the codes some time this week.

Thanks again for the direction on this.

 

The flexible joints at both ends of the big air tube from the AFM to the Throttle Body are known for developing cracks/breaks in them. This allows a lot of unaccounted for air into the system, and really messes things up. They are fairly readily available on the net. You may need to flex them slightly to see any cracks/breaks, if they exist.

Just a thought. This may have nothing to do with your situation, but it's something to consider. Something easy to check, too.
Good luck to you!
Pat☺