TPS & IDLE issue for 93 Geo Prizm

geo
prizm
#1

93 Geo Prizm, 1.6L, has NO EGR set-up and NO DashPot. put in a new TPS and I can’t get it to set right. Either sets better for idle or sets better for driving, but still horrible in lower gears. Choking on gas. No matter what ohm settings I put it at, even if I do it by ear. Checked IAC valve with ohm meter - okay. Throttle plate seems fine opening and closing. No air blockages. Going to re-check the vaccuum hoses tomorrow, but were fine a few months ago. However, hooked up a tachometer and my rpms are at 1000-1100 at idle and it should be 750 rpms. RPM’s DO jump up the correct ratio when jumped with the wire, but also about 250rpms too high as well. How do I adjust the idle?? Haynes manual says it’s factory set but also says that a screw does exist somewhere. Dealers are clueless (Toyota and Chevy.) Timing is perfect as well. Any clues guys??

#2

You could have a bad part. If it has elongated mounting holes, you may have to turn it but you probably have been doing that. What happens with the old TPS?

#3

okay, here’s an update on this. Did a vaccuum check and no leaks. Needle holds perfectly steady at 20" Hg with no drops or vibrating. However, when I rev it up and then take my foot off the gas, the reading does NOT go down to almosst zero - in fact it only goes down about 5"Hg. It does spike up to about 24"Hg before settling back to 20"Hg when I take my foot off the gas like it’s suppose to. But it’s the fact that it doesn’t go down when I accelerate that concerns me. Why is this happening? SOMEBODY PLEASE HAVE AN ANSWER - THERE ARE NO MORE PEOPLE IN ALL OF L.A. THAT HAVE A CLUE!! PLEASE!

#4

On reading vacuum indications, read this: http://www.autospeed.com.au/cms/A_2393/article.html?popularArticle
And, this: http://www.international-auto.com/fiat-lancia-tips-on-reading-gauges/tips-on-reading-gauges-vacuum-gauges.cfm

#5

Hellokit!! My darling, where have you been. Yes, I know how to read a vaccuum guage and my Haynes Manual also contains the pictures and decriptions of the different readings. Here’s a quote from one of your articles about my problem:

“When you floor the accelerator pedal, you can watch manifold pressure (another word for vacuum) swing from strongly negative to nearly zero (atmospheric pressure). When your engine is “on the overrun,” like using engine braking down a steep hill at high RPM, you’ll see really high vacuum readings.”

I have been reading past posts of yours around this problem, so tomorrow I am going to do 2 things: Pull the throttle body to double check it and clean it (again) and as many hoses as I can find and blow them out just to be sure, even though the vaccuum check says all is fine as far as leaks. Then I’m going to disconnect the exhaust pipe ahead of the cat converter and see how it changes things. I have long suspected the converter they gave me was the wrong kind or just bad ever since they put it in - about 1 1/2 years ago. Any further info or ideas would be great. Would a cloggged converter cause idle to be soo high? Do you know where the idle screw is? Will I find it when I pull the throttle body? Thanks for answering. I was hoping you would. You saved me months ago with your diagnosis of my ignition coil.

#6

You’ve got a Mulligan stew, here. You need some order. Start, and perform each check completely…No jumping about. Write the checks and findings in a notebook.
The throttle plate adjustment was good for 25 years. Do you think a mechanical setting has changed? No adjustment procedure is given for the throttle valve because none is needed (and, it is illegal to change the factory setting).
Idle rpm is set by the engine computer. The engine computer uses a few criterior for what rpm to set the idle speed. It will increase idle speed when the power steering idle-up switch is closed, by the electrical load idle-up, (more?).
The vacuum value falls only 5" hg. when you raise the engine rpm, and let the throttle close, right? Is the throttle plate closing quickly and fully? If yes, air may be bypassing the throttle plate. Where? An wide open idle air control valve, egr valve wide open, leakage around the throttle body.
Your repair manual should tell you how to check these things.
You don’t have to disconnect the exhaust pipe to check for blockage. Use this article, and click on the green strip Scenario 14. http://www.international-auto.com/fiat-lancia-tips-on-reading-gauges/tips-on-reading-gauges-vacuum-gauges.cfm
Use these Repair Guides to, ahem, guide your repairs: http://www.autozone.com/shopping/repairGuide.htm

#7

Okay, I pulled the throttle body, cleaned again and checked everything (hoses, stop screw, held up to sun to see if plate closing fully - it does and no leaks, snaps shut quickly, put in new gasket just because it’s cheap, cleaned air bypass holes, cleaned as much of the intake as I could reach cuz could get those stupid screws off the top of the air intake manifold.) Reset the TPS and did the vaccuum check again. Same exact readings. If there was a vaccuum leak, it would show up on the guage and not run in normal range and/or not have a steady needle. It DOES run in normal range with a steady needle. I truly think it’s the cat. converter. If the car can’t breathe, all that muck is backing up into the system and choking it. I just did a search on here and found my old posting about it chugging in the lower gears. Thank goodness it’s still here because I may need that as proof to get a new converter since the warranty ran out while I’ve been dealing with this SAME problem since MAY. Now it’s so bad it’s affecting other engine stuff. Since this thing really went caput a few weeks ago, my radiator fluid turned instantly and totally brown, the throttle body was so black - several millimeters of gunk on it - and it was spotless before this and the antifreeze was green. I flushed it of course. Ever since they put that thing in last summer, I’ve suspected it was the wrong kind or something even when I left the parking lot. Now they’ve cost me tons of money and time and stress. They better replace the damn thing. Shouldn’t converters last more than a year?!?! Hell, my original one lasted 15 years!
PS - I don’t have an EGR valve.

#8

Okay, here’s an update. THERE’S GAS IN MY INTAKE MANIFOLD! Also gas in my oil - the stick stinks and “oil” is runny. However, my plugs are just fine, no gas smell and look great. Whatever went caput sure screwed things up. As said previously, it fouled up my radiator fluid and gunked my throttle body, too. I pulled the air intake plenum today and there were puddles of gas sitting at the bottom. So now I need to get a new PCV valve cuz gas got through that hose into the valve. Would an exhaust back-up cause gas to be pushed backwards and up around the bend of the intake manifold to pool up like that? If you read previous posts here, you’ll see that I get a very steady needle on the vaccuum guage in the normal range. I believe that’s suppose to mean my engine has no leaks or stuck valves and stuff. The plot keeps thickening, guys! Who’s got the magic answer??

#9

And what can I use to clean the intake manifold? I’m afraid to use throttle body cleaner mixed with gasoline - it might explode!

#10

There’s too many Muligans in your stew for me…too many areas of activity.
To tackle a couple of items: The brown gunk in the cooling system is engine oil. Engine oil can get into the cooling passages, where?
Pressure check the cooling system. The intake manifold, or cylinder head, may be letting oil be pushed into the cooling passages. If you’re lucky, the leaks are where parts mate, and a gasket may fix it.
The throttle plate shouldn’t close completely. Think throttle plate in a carburetor bore. This is one reason the throttle plate isn’t after-manufacture adjustable. The engine control computer has to have some constant to act as a basis for its operation. The throttle plate opening is one of those basic basises.

#11

What do you mean “the throttle plate shouldn’t close completely”? A few posts ago you said it should close completely. There are tiny air bypass holes built into the throttle body. Isn’t the throttle stop screw supposed to be set so that the throttle closes completely?
What gaskets should I focus on replacing first? Any particular tests I can run to figure out which gaskets are leaking? If it is a gasket?
I will pressure check the cooling system as you suggested and let you know what I find. Thanks for the feedback.

#12

The throttle plate is factory set with an adjustment screw. It should close quickly when the throttle linkage is released. Check a new throttle body, at the auto parts store, with a thickness gauge. Then, you’ll know how near “completely closed” it left the factory, and what clearance you should set your throttle plate.
The “cooling system” includes the engine block, cylinder head(s), and, possibly, intake manifold. When pressure is applied to the cooling system, see if it holds pressure. If it doesn’t coolant is leaking somewhere, internally, or externally. Pull the spark plugs and see if any coolant is going into the cylinders. Look on the engine to see if any coolant is coming from some place.
The possibly leaking gaskets could be the intake manifold, or cylinder head(s) gaskets.
Are you sure you don’t know a mechanic?

#13

You guys are the only mechanics I know. this is Los Angeles - people don’t help people here. It’s $100 to just walk through the door. $50 just for a hoist fee. I’m about ready to get a job as a mechanic myself just to have access to tools I don’t have and a garage to work in.