October 21, 2005I've had this truck for about a month. The guy I bought it from got it at auction, had a new throttle body put on, and sold it to me. When I start it cold, the fast idle seems too fast, and seems to stay on fast idle too long. I'm thinking it could be the IAC, but shouldn't I get a service engine light for any emission/fuel system problem? And, yes, the light is good. BTW, it's an auto trans. Any ideas, I'd appreciate hearing them. Thanks.
Forums : Engines-Gasoline : '88 4.3 with TBI (117 Views)
October 21, 2005Ideas!
Yes, maybe. Do you have a Haynes/Chilton book?
I forget the name of it at the moment, however you have a choke type device in your snorkle, air intake. Take off the rubber hose connected to your snorkle and look for a flap. When the outside air temp is cold, the flap will close off the opening in the snorkle. This forces the fresh air to be drawn from the ducting hose that runs up from the exhaust manifold. Round silver cardboard looking thing connected to teh bottom of the snorkle and top of the exhaust manifold. As the metal spring that controls the flap warms up, it opens the flap to draw more fresh air from the rubber hose end of the snorkle. At least it is that way on my '87 2putt8 engine.
IAC is a possibility.
Check the front of your Haynes/Chilton book for cold starts. Look for anything related to a choke. The choke controls the amount of air gas mixture during cold starts. Colder it is, the richer the mixture (more gas), as the air warms up, less choke, more air in the mixture. More gas in the mixture makes the engine run at higher rpms.
Clear as mud????
October 21, 2005Knock that little flapper out of there and plug the hole so you get air from the fender.
October 21, 2005Thanks for the responses. I wasn't aware of that flapper in the air intake. I'll check that in the morning. Something I forgot to mention in my initial post is that I'm missing that pipe from the exhaust manifold to the air intake box. I figure that's related to the problem, and I've been trying to find something to put in there. No luck in junkyards and haven't been able to find any 1 1/2 inch flex pipe, but may settle for 1 3/4. It should help if it's stiff enough to stay in place.
October 23, 2005High idle speed sounds a lot like a vacuum leak. Check the vacuum hoses for cracks or anything disconnected. Should be four ports on the front of the TBI and one on the rear, and a vacuum fitting on the passenger side of the intake manifold.
If that's not it, it could be IAC, TPS, or MAP sensor issue. Start with the cheap fixes first, though!
October 23, 2005I agree with matt, an intake leak will lead to a high idle, check all your vacnum lines, If a line is broken it should throw a code... but they can still be dry rotted or something. Another question, does the high idle ever go away, say after like 20 mins idilng, or if you start the truck when it's warm?
October 23, 2005Thanks for posting. The excessively fast idle is only when I start it cold, and then it slows down to what seems to be normal, but not until 10-15 minutes after reaching regular operating temp. The defroster will be putting out hot air long before the idle slows. I guess I better buy/borrow a tach because I'm judging this long fast idle speed/length in comparision to my Toyotas. I don't think its vacuum since it does slow way down. I'll get to town tomorrow and stop by an auto parts store for a tach. Later today I'll break out the WD40 and check for vacuum leaks anyway. I'll post the idle speeds tomorrow night. BTW, I do have a Chilton's. Still wondering if this truck shouldn't be throwing a code if it's a sensor or the IAC???? Also, a guy told me at breakfast yesterday that the IAC should be replaced when the throttle body is replaced. Any validity to that?
October 24, 2005Auto parts stores should sell that little vent tube.
I noticed the other day that my plug wires above that hole in the exhaust shield are getting cracked. I need to install that vent myself, or move the plug wires. Check that out on your as well. In mine it shows up as a hesitation in the engine.
October 25, 2005I put the preheater tube on the truck last evening, and when I started it this morning it seemed to get off fast idle a lot sooner, so I'm going to mark it "fixed". Never thought of parts stores selling that. I have to start thinking more "universal". Thanks for the tip on the parts store, Hanr3.