Hi guys, I haven't been able to find a similar problem anywhere on the forums. The problem is this: I replaced all the exhaust gaskets on my 88 4WD Pickup and everything runs/sounds 10x better. I even feel maybe a little power increase. Although there are good effects after the overhaul, there are some suspicious ones as well. Now the truck seems to idle a little higher and when I hit 70-75 the throttle response is delayed by a 10-20 seconds. Is this a built-in governor? Or do I need to switch something in the MAF sensor? Any advice is appreciated.

Side note, the throttle delay didn't occur at 70-75 before I redid the exhaust. Truck is new to me since July.

 

Which engine do you have? Please place your vehicle info on your signature.

 

Hey, sorry. Rookie mistake. I drive an 88 pickup 22RE 4WD.

 

High Idle, Delayed Throttle response, did you mess with the TPS at all?

 

I haven't messed with the TPS yet. It's not stalling on me or bringing up a check engine light .... yet. But you're right, the other symptoms point to the TPS. Is there a way to adjust it? or does it require a full replacement/resetting?

 

They can be adjusted,

 

Thanks for the link. I'll give this a try! Much appreciated!

 

A much more likely scenario than something you didn't touch is that your exhaust is plugged up like your catalytic converter is clogged or a pipe is collapsed

 

A coworker thought maybe I bumped a vacuum hose, but all those are on the other side of the engine. The throttle response was "ok" at high speeds before I added the gaskets. Wouldn't you think if it was in the exhaust these symptoms would have occurred beforehand too?

I will likely replace the exhaust in the future anyway. I believe it to be all original

 

Absolutely nothing AFAIK. Take off the cat and everything from the cat back (or leave it hanging) and go annoy some neighbors. Is the delay gone?

Should have nothing to do with speed either? Automatic transmission?

75 is kinda the useabl top speed, not sure if anything will respond. On my truck there is not really any response after 60. But there is a response - in tone motely, not in forward momentun. It takes it's darn time, will hit 100 in 39.5 miles or so


When you say response, what do you mean exactly? You step on it, and 30 seconds later it gets louder and starts to move?

Is your throttle cable correctly placed? At the rear of the engine, it should be wedged into a sort of "holder" tab.

Can you do a soundfile? Video?

 

Easy enough and cheap to check, get another doughnut gasket for the intermediate pipe and loosen it from the manifold so it leaks there if it's back to the way it was after you know it's exhaust related.

If you haven't done so already you might want to reset the ECU trim memory.

 

The cable is secured on both ends by the seathing, that clip is there only to make it look nice and keep it off the exhaust.

Definitely a video would go a long way here.. (The description is kind of vague)

 

If it's not on that clip, it will break at the firewall. (not the cable itself) - then you have a throttle that doesn't do anything for 1/2 it's travel.

If it's not on that clip, it can get caugt by something and you have a racing away engine. You give it gas, and when you shift it redlines until valve float...
Ask me how I know. Lucky I had some space and thought of turning off the ignition fast.

 

Sorry everyone. First time posting here, so I'll try to clear up some details. The truck is a 5 speed standard. 1-4 work smooth and no delayed response. 5th is the issue and only at 70+ mph. I'll give a scenario. I drive 55 miles over the weekends to visit my parents. All highway speed. 30 miles of 65-70 mph in 5th gear works fine. No throttle delay, everything is working fine. I've even got up to 80 and it was fine (felt like that was about the max I wanted to try). Once I hit that 30-40th mile of the trip it becomes harder to maintain 70mph. I have to press more gas than the previous 30 miles and it will delay ~3-10 seconds and then jolt forward like I put my foot to the floor. So it feels like a yo-yo for the last 25 miles of the trip. Pressing gas, engine waits a few seconds then shoots forward, then let off gas to fall back to 70mph, rinse, repeat.

Now I've never driven a 30+ year old vehicle before. Could it just be normal? I'll try resetting the computer since that seems to be the cheapest route. Then I'll try with the exhaust. Figured I'd build up some opinions and flesh em out before I get too hot and heavy into engine repairs. I appreciate all the feedback and help I'm getting though. I'm somewhat new to the auto repair world. These little trucks seem to be a great first step for me.

 

I'll try getting a video of the symptoms. Also forgot to mention again that it seems to be idling high, though I have no tach, so can't be 100% sure.

 

Does it have cruise control, and is it on?

It's not normal. But there are no sensors for what gear you are in, so - there is no correlation between the lag and the gear you have in it.

This some crazy weird behaviour

 

No cruise control, unfortunately. That'd be great for that drive. Been spitballing ideas with guys at work too. They all agree a good ol reset would probably help. Been busy so haven't had a chance to mess with it. Have some time tonight, then I'll test it over the weekend again.

Thankfully I'm not crazy. I didn't think it was normal behavior, but if it was I would have felt bad posting out here lol.

 

Might start with the throttle and air flow meter tests, they're free. Measure the resistance on VTA on the tps while you sweep from closed to open throttle you should have a nice smooth curve no glitching, I don't recall off hand what it reads at full open since I prefer to do the voltage test instead. You also want to inspect the throttle plate movement is smooth and it reaches fully open.

You will do the same/similar tests to the VAFM, a slight difference here is you might get a not so smooth curve with a glitch "in the avg rpm range" where the sensor is a bit worn out (they designed a fail safe so it's not a big deal like it would be if your tps went to half way and dropped back to zero).

Your likely hitting large hills the last portion of the trip? Overdrive is meant for cruising I wouldn't try to climb any big passes in it, nor expect to keep up with something with twice your horsepower. Lots of these are happy to hit 60mph, remember thirty years ago the speed limit was 55 almost everywhere.

You may also be hitting a load point where the clutch is starting to slip. Do the rpms shoot up right before you start to feel the acceleration?

 

This is very good thinking. A hill I cannot see (slight incline) would rob the truck of "any" accelleration at 70 / 75 mph

 

Yes, there are hills along the trip. I paid extra attention this past weekend and it did seem to happen more around hilly areas. I also had it happen going downhill and on a "flat" stretch a couple of times. the strange thing is that it's only around 70. If I go 75, it's fine, if I go 65 it's fine. I reset the computer and it didn't change, so I'll give these sensor tests a try next. It does seem like the RPMs "spool up" before it finally decides to accelerate. Thank you for these theories. I believe we're narrowing in on the issue.