Hello All,
I have 96 with 3.9 automatic. I have been slowly changing out all of my sensors, and with each one she runs a little bit better.

I noticed that when I would be sitting idling, 2 things: one sometimes when I would take off the truck would hesitate a lot, revving the motor would usually help, or actually letting off the gas and then pressing it again.

the second thing is I noticed the idle seems a little off, fluctuates and sometimes makes a weird mechanical sounding noise coming from the engine compartment.

Anyway, I went with a bad IAC, and when I changed it, the rpm s went up to 2500 and held with some fluctuation. I put the old one back and the problem went away.


Do I need to disconnect the battery to reset the computer, or is there something else wrong.

thanks in advance

 

Yes reseting the battery can help. But most likely the new one is bad. Lots of new ones are bad. Since it sounds like your old one work just use it.

 

ok got it,
But If I leave the old one in, then I still have the problem with hesitating from idle, unless you think it may be something else.

 

It might be something else. You can return it and try another. One guy returned them 3 times until he got a good one.

 

I was thinking the hesitation was a bit like the hesitation one would get from a bad TPS, which I had changed not too long ago. But she ran a bit better after changing it, anyway, I put the old TPS back in and so far it is not hesitating, but when sitting idling for long period of time, the idle goes like she wants to stall.

I dont know. Can someone just make it run like new with the wave of a wand?

I feel like I am chasing sensors here.

I also recently changed my O2 sensors, and now I get an error saying its my High voltage O2 sensor #1, but it comes and goes. Could this have something to do with it?

Do O2 sensors come bad often?

Thanks
P

 

Engine bogging is usually from a change in vacuum pressure from the crankcase to the atmosphere/intake side. Where the engine is not "catching up" with the fuel requirements of the acceleration. TPS sensor develope a "blind spot" from repeated use, as they are based on resistance (much like the fuel level sending unit). A bad TPS would always (95% or greater) have the same blind spot during acceleration depending on the throttle position. The coolant temp dictates the mixture prior to the engine warming up. The O2 sensor also affects the mixture, but after a minute or so (after it warms to 600 degree's+/-) so without a better understanding of how your engine is performing, you may just be chasing sensors. While this info is fairly accurate, and I am not trying to be a tard, explain a little more about when, how, your engine is "bogging".

Not to mention a loosened timing chain, loose distributor (in relation to the crank sensor) can affect the advance of the cam which can contribute.

 

Great,
I changed the timing chain and sprockets so that is good.

The bogging does not occur all the time. when it does its like there is not enough fuel and power drops to next to nothing. If I pump the pedal a couple of times I can get it to go again, and then no problem for a while.

Since putting back the old TPS, it has not done it, but I can feel the engine is not running at 100% its like an old lady on a cheese diet, but it is a subtle difference in the two. that is the old TPS with the new TPS as opposed to an old lady on a cheese diet and engine running at 100% LOL, sorry, I kill me.

The engine is old, she has 205k on her, but I am in denial that she is not able to run better. I am waiting to see if the bogging comes back with the old TPS, if it does not, then I will return the new one.

What about the IAC? do you think that is a waste of time to change? Mostly the engine idles fine, is that all that that controls?

 

The IAC is named for what it does (Idle Air Controller does not put any data out if the TPS is above the minimum). I assume that your bogging "under load" as opposed to idleing. They are very differing aspects. When you change sensors, you must ALWAYS reset the ECM (IMO), otherwise you have to go through the learning period from the old sensor data. My block had over 200k, but only required a berry hone to true the cylinders, so mileage is not the only prerequisite as far as wear. Back to the bogging....
I, personally, think you have a vacuum leak, or rotted hose, or similar. You did not mention wether the engine temp was a factor. What do your plugs look like? Short trips can foul the plugs also.

Since the old TPS and the new TPS have differing driveability qualities, I would think you got a bad sensor, but it definately is suspect since there is such a drastic change.

 

Engine temp is good, and I have not checked my plugs since I put new ones in 3 months ago.
The vacuum leak may well be it, it responds randomly as a vacuum leak might do if it was a cracked line.

Old school used to use ether to spray on the lines and listen for a rev increase, are there new ways to check?

thanks

 

Yes, the "old school" way is pertinent. You can remove the vacuum lines and bend them to check for cracking. Beware that doing this may break them, but they would need replacement anyway under the circumstances. When I asked about engine temp, I was referring to the bogging occuring at low temp/ starting temp or at normal operating temp. Checking plugs quarterly is part of routine maintenance, and to see the effects of the engines stoichiometry. Being new isn't what spark plugs are for. They help to "listen" to your engine (ie fouling, lean condition, seals, ect.), and make judgment calls for other types of possible maintenance.

I am going to make a soapbox announcement, and say that modern generations look at vehicles like a means to get from point A to point B, and when their vehicle lets them down, they get frustrated. A vehicle is no different than a horse of years past. Letting the horse go lame only affects the families well being and certainly affects the potential income of the owner, if used for business purposes. It is important to know your vehicles design limits and make efforts to maintain the vehicle to its potential. A vehicle is very costly to maintain correctly, just like a horse.