Bad MPG and hesitation on 90 4cyl help!

[Sharkbite86]

I searched the forums and found other people with similar issues but I could not find the answer I was looking for:

My 1990 4cyl camry has about 250k mi and gets about 24mpg city and 27hwy and while that is not horrible its not that great for a 4 cyl camry. I also get this weird hesitation at stop signs and only happens in first gear. Right around 1500rpms the engine will suddenly loose power but then get it back after 2200rpms. Im stumped as to what's up. I've run many tests and still cant figure out what the heck is going on.

I know my car is running rich because I can smell it out the tail pipe, and I also checked the output from the O2 sensor (idle O2 sensor voltage is around .7v -.9v and should be .5v). I replaced the fuel filter, checked the fuel injectors, fuel pressure, spark plugs, ignition system, and the EGR system (but not the charcoal canister). The clutch is shot, and so is the suspension (but I dont think they would give me a whole 10mpg less than what I used to get, right?). I am using an after-market cone air filter but the problem has been around longer than that has been installed. My car also burns a little oil through the head but not a whole heck of a lot... Can anyone help?!!
Thanks in advance!

[Kep]

My inclination is the IAC valve. When cleaning this I like to recommend removing the , throttle body, IAC, EGR, EGR modulator and cleaning them all. This should not be a major deal if you are reasonably handy. The IAC and EGR will likely be packed with crud and need to be carefully picked out (dental picks work pretty well) and cleaned. The throttle body can be cleaned with throttle body cleaner (read the label to make sure that it is safe for the throttle body plastics) and a tooth brush. Check the vertical tube that the EGR is mounted on as well as the rubber tubes to the modulator (I think this is the "solenoid" mentioned above). If you have done this before I expect that it will take most of a day to do this. If you haven't, plan on all weekend. Read up on disassembly and assembly first.
When you get some more time,after you put it all back together, run some SeaFoam through the vacuum line to the throttle body to try and clean the interior of the engine. Put SeaFoam in the gas tank at a fill up and it will help clean other parts of the engine. About a day before you change the oil put SeaFoam in the oil and drive around for about 60 - 100 miles before you change the oil.
It is a process but after you are done your engine should be nice and clean and run better. You can do searches on this forum and the GEN 3-5 forum for several good posts with step by step proceedures and pictures.
How did you "check" the EGR & ignition systems?
When we went over to ethanol we lost about 10% of our mpg. I just hope that it is better for the environment because it sure isn't better for my pocket book!!!!!!!!!!! I understand that the newer cars are timed differently to allow for the difference in combustion. Does anyone know if it would be feasible to somehow reprogram the ECUs in our older cars to run better on ethanol?

Kep

[atobe]

only toyota would know how to reflash it.. but i thought ethanol requires high compression... the 3sfe is a measily 9.3:1 ratio... where ethanol runs better at 11:1 ratio


anyways you can try replacing your O2 sensor.. or hit it with a blow torch. and try cleaning out your intake like he said.

[white90dx]

I didn't see the ignition coil specifically mentioned. You may want to check/replace it as it is known to crack. Also replace your O2 sensor.

-Charlie

[white90dx]

Originally Posted by Kep

When we went over to ethanol we lost about 10% of our mpg. I just hope that it is better for the environment because it sure isn't better for my pocket book!!!!!!!!!!! I understand that the newer cars are timed differently to allow for the difference in combustion. Does anyone know if it would be feasible to somehow reprogram the ECUs in our older cars to run better on ethanol?

Kep

Bump up the ignition timing a bit (2-4 degrees) if you are always going to be running ethanol oxygenated fuels. Make sure to listen for knocking and bring the timing back if you hear any.

My WRX runs better (from what I can tell) with the ethanol oxygenated fuels, but it has a nice adaptive ECU with a knock sensor to keep timing as advanced as possible/safe.

-Charlie

[Sharkbite86]

Originally Posted by Kep

When you get some more time,after you put it all back together, run some SeaFoam through the vacuum line

how do you mean? Just take out the vac lines and pour some SeaFoam through the lines? Maybe I should just replace them altogther...

Originally Posted by Kep

How did you "check" the EGR & ignition systems?

I did a vacuum test to make sure the valves opened at the right time. Simple test by pumping air into the vale to see when it opens.

Originally Posted by Kep

When we went over to ethanol we lost about 10% of our mpg. I just hope that it is better for the environment because it sure isn't better for my pocket book!!!!!!!!!!! I understand that the newer cars are timed differently to allow for the difference in combustion. Does anyone know if it would be feasible to somehow reprogram the ECUs in our older cars to run better on ethanol?

I don't think ethanol is better for the environment if you ask me. I am all for eco-tech but this is just a waste. Ethanol has about half the heat energy as regular gas and is not as powerful. Your car may produce fewer emissions but you actually create more emissions in total due to farming and processing. The numbers simply don't add up with pure Ethanol

Originally Posted by white90dx

I didn't see the ignition coil specifically mentioned. You may want to check/replace it as it is known to crack. Also replace your O2 sensor.

-Charlie

I did a spark test on my car not too long ago where I disconnected the plug on one cylinder at a time and attached a spark meter (load) in place. I still get a good spark at 20-30,000 volts so my coil is just fine.

[Sharkbite86]

Okay so today I was able to clean the throttle body with some carb cleaner. Wow was there a ton of crud in there (and the whole damn manifold looks the same). While the engine Idles WAY better (it's quiet now and does not rattle anymore) the engine hiccup deal is still there. Don't know about MPG yet but I imagine it will be the same.

I have not had time yet to check the EGR but Im wondering, would that would even make any difference with MPG? All the EGR does is lessen NOx and CO2 emissions. I mean as far as I know the core problem here is the rich fuel mixture, so what could be causing that?

For now though, I will replace the O2 sensor tomorrow and see if that helps. Thanks guys

[argojos1]

how much would a o2 sensor lower you mpg

[Sharkbite86]

Originally Posted by argojos1

how much would a o2 sensor lower you mpg

dunno, but if the O2 sensor is reading wrong it could trick the ECU into dumping fuel into the engine... but the O2 sensor read high so I don't think that could be the issue either

[TBayToyotaBoy]

Not to hijack your thread, but as far as ethanol is concerned: I think much of the reason there is a push to switch-over is that it will extend the life of world oil stocks--NOT so much because it makes environmental sense.

With ethanol, we wouldn't have to radically alter our oil-based infrastructure for awhile longer, and the only ones to suffer are peasants in mid-low wealth nation states (as their food corn is diverted to ethanol production). See the Mexican riots for an example.

[argojos1]

would a bad o2 sensor make air fuel ratio mixture wrong

[Sharkbite86]

Originally Posted by argojos1

would a bad o2 sensor make air fuel ratio mixture wrong

Yes most definitely. As I said before, if the O2 sensor is reading the oxygen in the exhaust wrong it can affect fuel mix easily. The vehicle computer looks at the O2 sensor to adjust fuel mix, if the sensor reads low O2 (lean mix) the computer will add fuel, if the sensor reads high O2 (rich mix like my car) it will lean the mix... only trouble is my ECU is not leaning the mix and is ignoring the O2 sensor for some reason... If the computer thinks a sensor is wrong it will ignore it (if it can) and do whatever the default settings are. I don't know why it is doing that on my car though.

[Kep]

Sorry that I didn't get back sooner. Sharkbite86, if you put a vacuum to your EGR (on & off a couple of times) and it always worked then it is probably OK. However, it isn't very hard to clean in there. Pull the air hose from the throttle body and if it is dirty the rest is probably also.

Sea Foam (do searches for Sea Foam and Seafoam) is a popular topic in the GEN 3-4 forum. Much more so than in this one I think. To the point, go to the next link to see a photo of which vacuum line to sip the Sea Foam into:
http://www.toyotanation.com/forum/showthread.php?t=219112&highlight=seafoam

For an ad-nauseum discussion of the pros and cons check out:
http://www.toyotanation.com/forum/showthread.php?t=179324&highlight=seafoam

For Sea Foam's own WEB page description see:
http://www.seafoamsales.com/motorTuneUpTechGas.htm

A good youtube video of the Sea Foam process (he uses the connection at the brake booster, I use the one closer to the throttle body - same hose just a different junction):
http://www.youtube.com/watch?v=KhPsL-6VjLc

That should give you a pretty good DIY Seafoam review.

Consider checking the resistance of your plug wires and the center point of the distributor cap (Though I find that half the time I remove the wires I damage one or more of them.).

Depending upon how shot your clutch is it may be contributing significantly to a milage problem if it is slipping while you are traveling.

I am still focused on the IAC and EGR. Mainly because those were my problems so they may have nothing to do with your situation.

Kep

[Sharkbite86]

Originally Posted by Kep

Sorry that I didn't get back sooner. Sharkbite86, if you put a vacuum to your EGR (on & off a couple of times) and it always worked then it is probably OK. However, it isn't very hard to clean in there. Pull the air hose from the throttle body and if it is dirty the rest is probably also.

Sea Foam (do searches for Sea Foam and Seafoam) is a popular topic in the GEN 3-4 forum. Much more so than in this one I think. To the point, go to the next link to see a photo of which vacuum line to sip the Sea Foam into:
http://www.toyotanation.com/forum/showthread.php?t=219112&highlight=seafoam

For an ad-nauseum discussion of the pros and cons check out:
http://www.toyotanation.com/forum/showthread.php?t=179324&highlight=seafoam

For Sea Foam's own WEB page description see:
http://www.seafoamsales.com/motorTuneUpTechGas.htm

A good youtube video of the Sea Foam process (he uses the connection at the brake booster, I use the one closer to the throttle body - same hose just a different junction):
http://www.youtube.com/watch?v=KhPsL-6VjLc

That should give you a pretty good DIY Seafoam review.

Consider checking the resistance of your plug wires and the center point of the distributor cap (Though I find that half the time I remove the wires I damage one or more of them.).

Depending upon how shot your clutch is it may be contributing significantly to a milage problem if it is slipping while you are traveling.

I am still focused on the IAC and EGR. Mainly because those were my problems so they may have nothing to do with your situation.

Kep

Well cool stuff . So I did the Seafoam clean thing today and wow was there a ton of smoke haha. The car runs just a little bit better than before but I still have that hesitation ... I will take a look at the IAC and EGR when I get the chance. I am also going to look into my O2 sensor. My clutch is pretty shot but I don't actually feel it slipping while accelerating, but it IS the original clutch ... even if it is the problem could it cause a hesitation like what I have? I looked at my air-flow meter as well and it seems ok but one of the resistance tests seemed off... could my airflow meter cause the hesitation though?

haha I feel like I am going to replace every part in the car before I figure out what's wrong . Thanks again

[Kep]

The driver has a lot more to do with a "shot clutch" than the milage does. Why do you describe it as "shot"? I believe one test is to put the parking brake on and let off on the clutch in second gear. If it kills the engine right away, no problem. If the engine dies after the midway point then the clutch is getting bad. If the engine keeps on running...well... the clutch is shot. I may be wrong about which gear to select. Someone else will chime in if I'm wrong.

You say that you made a resistance check on the MAF that was "off". What was the test, what was the expected result, and what was the actual reading? The MAF is giving the ECU air volume data to determine the fuel to air mixture so if it is off it will have an effect on how the engine runs. The "D" looking top is a plastic cap held in by a kind of silicon caulk. You might want to gently pick out the silicon (there is a plastic lip under the silicon so don't press real hard) and lift the top off to make sure that it hasn't gotten all dirty inside. Don't make any adjustments without first taking some pictures and making a lot of notes so you can always put it back the way it was! I personally don't feel that any adjustments should be made since it will be at factory specs, however, there have been some threads on adjustments that were thought to be helpful.

I'd be much more focused on the throttle body, EGR and IAC.

Kep