Hesitation under load, and other things

[landshrk]

I have a '94 4-Runner, V6, 5-speed, 4WD. 200,821 miles. It hesitates, badly, while accelerating, even if it's just the engine revving up. If I put a constantly accelerating rev on it, about half the time it'll rev up smoothly, return to idle (which is sitting at a fairly constant 1050 RPM or so, unless I have the headlights on, where it'll drop to just under 1000 RPM), and then let out a little "whoomp." The other half of the time, it acts as described below.



If I only rev the engine up to around 2500 RPM, or really, any other level and let it sit there, it'll sputter and fight, making those hollow "whoomp" sounds the whole time. The sounds are not at regular intervals, but rather, at random.



Once it has warmed up, the engine has a VERY faint, but still perceptible (at least, to me) loping. It's so faint that it doesn't even register on the Tachometer, which is still reading a constant 1000 RPM.



I have a few ideas as to what this might be, but I want to see what the TN Collective Mind has to say about it. Anyone else experienced these problems? Any ideas as to what it might be?



The vehicle has been through a number of owners. The last guy who had it did an entire engine gasket job, and I drove it three hours home, and for many months after with no problem. As far as I know, there have been no major mods to the vehicle. I do know that the EGR valve has been disconnected, but it's been that way since I bought her, and when I reconnect it, it makes the engine run like total sh*t, loping at idle really bad. There was a fuel leak a while ago, but it's been fixed.



I can't think of any thing else that might help someone answer this. If you need any more info, please PM me, or just post it in this thread, as I'll be checking back frequently. Thanks so much for all your help!

p.s. in case you couldn't tell, this is very frustrating.

[jetwhine]

Landshrk,

First off I would suggest fixing the EGR valve issue. That sounds like it may be a faulty valve but some trouble shooting may be involved.
My first question is what type of spark plugs are in your rig. I know this may sound funny but if you are new to Toyota's this is important. They must be either Denso or NGK. No others will do. And also do not and I repeat do not have the parts guy say you can use a substitue number. The numbers are located in your owners manual. If you don't have one call the dealer and get the numbers from them. If your parts guys don't have them go to someone who has them or just get them at the dealer, they are not expensive.
Question 2- Did this issue come up after a recent fuel up?
You might want to also do a compression check/ leakdown test to check the quality of the rebuild.
The valve clearance might not be right also.
And worst case cenerio other that another blown head gasket is that maybe by some chance your timing belt may have jumped a toooth.
So the spark plugs are the first thing I would look at. Then check the other things and then I would make sure that the Throttle position sensor is set correctly at idle. You will need a vacuum pump to check the idle positon.
Hope this helps

[fourwd1]

I agree with jetwhine. The EGR is not working properly, correct that and see what happens and go from there.

[landshrk]

I had a similar problem to this prior, though I was able to drive it. It ran fine, except at idle, where it would sputter and die, whether at freeway speeds or sitting at a light waiting. I replaced the EGR valve, and after much refab-ing of that metal tube that runs up into the bottom of the EGR (it was so badly rusted that we broke it uninstalling the old one), we got the new one in. It didn't fix sh*t. I ended up having to disconnect the EGR and insert a screw in the tubing (just to keep dirt and whatnot out), which fixed the problem entirely. I didn't have an issue for around 6 months, until this just popped up one day.

I have NGK plugs in, as that's what the guy at AutoZone told me I'd need, and what I'd read here and on Yota Tech. I gapped them myself, and installed them along with new wires, cap, and rotor. It all ran fine, until one day it didn't.

This didn't coincide with a recent fill-up. I always fill all the way up, and this current issue started around half-tank. I really hope it's not a blown head gasket, that's not something I want to deal with if at all possible. I was thinking the timing belt might have slipped, which would explain the engine missing, the lack of power, and the suddenness with which this all happened. The TPS should be fine, as I see no reason why it would just get itself out of whack all of a sudden...

I'll check the spark plugs, and see if I can't get a timing light over here...

[jetwhine]

landshrk,

As far as the EGR valve is concerned, there is more to it than just the valve. Have you checked for stored check engine codes, even though you don't have a check engine light there might be a stored code that might help fix the EGR system. Knowing that the engine has been taken apart that makes me suspect of some possible crossed vacuum lines on that system. Anyhow the timing belt is fairly easy to check just pull off the top covers and verify that your marks all line up.
The TPS should be fine. That's not a good statement. If you have not checked it then it might not be fine. It may look fine, but be a wolf in sheep's clothing.
Another thought is that a bad Engine Coolant Temp sensor might be at fault. That will cause all sorts of problems with the running of the engine. It might not be flagged by the CEL. If it sends a signal good or bad the computer does not know that. It only knows when it quits all together. Maybe do some resistence checks on the sensor.

[tom1794]

I'm new to the site as well, and just posted my own problem (which seems to be a real "head scratcher"), but a leak in the air duct between air flow sensor and throttle body can cause a loss of power and the engine to "lope".

[jetwhine]

landshrk,

If those things suggested are ok, then I would do a cylinder leak down test to see if the internals are ok.
Also you might have a bad injector. You might try some injector cleaner. I like BG products K44. It works quite well.