1993 Camry 4 cylinder Losing Power Under Load

The car was running fine until I needed a new battery. I replaced the battery and shortly after, I noticed the car would have a miss and idle rough intermittently after putting it in drive. It's an automatic transmission. I took it out for a ride and when I tried to go up a hill it could barely make it. The car has about 90 K miles on it but it is very well maintained. It has new plugs, cap, rotor and wires with less than 10 K miles on the parts. I pulled the plugs and they looked good. I cleaned the throttle body and the IAC but it didn't help. There is no check engine light on. Not sure if I will get any codes. Out of gear it idles fine. I can rev the engine out of gear with no problem. It seems to be load related.
Also, can I download the service manual for this car from this site someplace?
Thank you for your help in advance.
I appreciate it.

Try replacing the ignition coil. They are known problems in this engine. Send me your e-mail for a FSM if I can find one.

My email address is frafreg@yahoo.com. Do you think a cold check of the coil with an ohm meter show any problems? I can check the winding if I know what it should read. Thank you very much for your help.

A resistance test of the coil would only tell you if it's bad, not if it's good. The coil operates under very high voltages and if it is bad, a low voltage test like with your VOM will not necessarily detect it. If the coil is out of spec at low volts, then you can be sure it's bad.

check your e-mail

Also, check if there are any codes stored in your ECM

Thank you very much for the service manual and advice about replacing the coil. I will get to this as soon as possible and let you know the results.

Hi Brian. I finally got around to replacing the ignition coil last night but there was no change. While the car was fully warmed up, I watched the car idle out of gear and I noticed an occasional misfire but when I put it in gear it stalls. I took it out again and I tried dropping it down to low gear when going up a hill and I was able to get up the hill. This all happens after being fully warmed up. When I originally cleaned the IAC I did it on the car by spraying into the two hole in the intake manifold. I didn't remove the IAC. Is it possible that the IAC is still dirty or maybe the throttle position sensor? There are still no codes. Any help much appreciated. Thank you!

Check the ignition timing in "N" gear, shorting TE1 and E1 terminals of the data connector. Should be 10 btdc at idle and operating temperature.
Check your fuel pressure in pinched-off return hose with ignition on, shorting FP and +B terminals of the data connector.
Check spark in all cylinders, should be bright hot snap and jump 1/2 inch.

These are the starting points from Basic Inspection on page EG1-310 of your maintenance manual. Follow that troubleshooting procedure. These are for a no-code situation. See also EG1-327.

Brian, thank you very much for your response. Since we spoke, I purchased the TOYOCOM device which enables me to see live OBD1 data. The timing is correct at idle, the ECT temperature looks good and spark is a bright hot snap. The only information I couldn't see that might be an issue was the O2 data percentages because I didn't have it set up correctly. I was told that oxygen feedback should be on when the engine is warm and the engine load is not heavy like cruising around town or just idling. It should indicate a value from 0% to 15%. A solid 20% means the system is out of range and inactive. I am going go back to make sure the percentages are correct. I noticed after warm up, the car idles fine in park but almost stalls when i put it in drive. If i disconnect the TPS, it idles good. I tried driving the car with the TPS disconnected but the hesitation under a load going up a hill is still there so I don't think the TPS is the problem. It is just compensating for something else I haven't identified yet. Also, i can see that the TPS operates smoothly without any skips while opening the throttle by hand. Appreciate any feedback you may have at this point. Thanks again!

Check fuel pressure and volume.

Hi Brian. I am going to rent the fuel pressure tool as you suggested but my local Autozone did not have one on hand this weekend so, I have to wait until someone returns it.
In the meantime, I took your advice and I went back to check the ignition timing again. The TOYOCOM make it easy to see the timing without a timing light. The timing is going up and down at idle from -2 to +5 in Park. The idle is moving up a and down also. I cleaned the IAC on the car and was wondering if I need to remove the throttle body and do a more thorough cleaning of the IAC since it may still be dirty. What could cause such an unstable timing? Thanks again for you help. Much appreciated.

Bad distributor, loose distributor, bad distributor cap/rotor. See if there is play in the distributor shaft. When is the last time you changed the timing belt tensioner? Crank position sensor. Crank position sensor star wheel may be marred. I'm not sure what level of damage to the star wheel will cause it to indicate bad on the sensor.

Still thinking...

Thanks for your reply Brian. I appreciate your help. When I replaced the coil I didn't notice any excessive play in the distributor shaft. The car has 79K miles and has had oil / filter changes every 3K to 4K miles. I swapped out the cap, rotor, wires and spark plugs to try to diagnose this problem a few weeks ago. Nothing made any difference. The plugs are Bosch. Not sure if that matters. Is there a way to test the camshaft position sensor? Thank you.

Bosch plugs are marginal. Use DENSO or NGK only. They are unlikely to be part of the problem since changing them had no effect. I wouldn't buy Bosch for your engine. DENSO and NGK only should be used for all ignition components.

I guess you mean the crankshaft position sensor. I don't know of a good way to test it. I would make a point of checking the distributor shaft carefully. Check for rotational play and side-to-side play. Make sure that it's tightened down correctly.

Fuel pressure. Check fuel pressure. Under load means more fuel is required and you may have clogged fuel filter or weak fuel pump. Even bad connector on pump.

Thank you for your reply. I noticed the timing was very unstable at idle after warm up. I'm using the TOYOCOM device which enables me to look at live data and it shows the timing moving up and down from about -5 to about -1 while idling. I tried to advance the timing to -10 degrees, rotating the distributor counter clockwise, but I was only able to get it to about -5.3. That was as far as the distributor could move. Although the timing is still wrong, the idle became smooth and the timing got steady. I took the car for a drive and there was no longer any trouble going up a hill with the car under a load.
I need to go back and check the base timing with a timing light and jumper TE1 and E1 in the diagnostic connector per the service manual. I suspect the timing belt may have jumped a notch, but I can't be sure until I hook up the timing light. Any thoughts would be helpful. Thanks again!

I doubt it is the timing belt. Bad valve timing would cause you greater problems than what you are seeing. The timing you see when you jump the connector will tell you the story. If your timing is stable and within spec, you are probably in good shape.

If your valve timing were off by one tooth on the timing belt, Changing the the ignition timing by rotating the distributor would not correct it. Check your compression to check if the timing belt is off by a tooth.

I adjusted the timing to 10 degrees btdc at idle with E1 & TE1 connected. When I removed the jumper, the timing went to 5 degrees btdc instead of 13 to 22 as described in the service manual. The bad idle returned.
I removed the vacuum hose from the fuel pressure regulator, held my finger over the vacuum hose and the idle returned to normal. I think the fuel pressure went up or at least closer to normal. Unfortunately, I was unable to check fuel pressure before or after removing the vacuum hose because I didn’t have the correct adapter to connect to the outlet of the fuel filter. Since the idle got normal and there is no fuel coming out of the fuel pressure regulator, I think the problem must be with the fuel filter or the pump.
I went online and I think I found the correct adapter.
Link to adapter:
https://www.ebay.com/itm/Banjo-Bolt-Fuel-Pressure-Tester-Adapter-Asian-European-M12x1-25-thread-Gauge-/251254996574?rmvSB=true#rwid

Any thoughts or suggestions? Thank you.

Anywhere from 0 - 10 deg BTDC is correct for your engine. Double check your service manual.

If it were your fuel supply, you would not be able to correct it periodically as you made changes. It would always be bad. Your problem may be with some sensor giving the ECM bad data, like your coolant temperature sensor or your manifold pressure sensor or crankshaft position sensor, etc. Perhaps your distributor is installed with the shaft indexed incorrectly. Remove the distributor and make sure you install it correctly, lined up with the #1 cylinder at TDC on the compression stroke.

I marked the position of the distributor on the outside, and the position of the rotor to make sure I put it back in the exact same position.
There is no separate crankshaft position sensor. The cam and crank angle signal comes from pickup coils inside the distributor. NE + and NE- is the crank angle and G + and G – is the cam angle. I checked the resistance and the air gap for both coils and they were good.
The only thing that gave me a smooth idle was removing the fuel pressure regulator vacuum hose while plugging the vacuum hose. That didn’t fix the hesitation under a load. Advancing the distributor as far as it would go corrected the hesitation under a load but didn’t correct the rough idle.
The ECT temperature looks correct according to the live data I see from the TOYOCOM.
I’ll go back and check the MAP sensor with a vacuum gauge to make sure the power output drop is correct at different levels of vacuum.
Thanks for your help. I’ll let you know my findings.

Did you check the compression? Is your engine operating temperature normal or is it low?

Is the intake manifold vacuum in the normal range at idle? Gasket leak in intake manifold? Bad vacuum hose connection, leaking vacuum system hose?

Since the battery change apparently started the problem (maybe), check the power wire on the battery (positive terminal) which is separate from the high-amp starter connection. If the connections or conductor are questionable, they are potential sources of erratic electrical behavior.

I haven't checked the compression. The engine operating temperature is normal. I will have to find out what normal intake manifold pressure should be at idle.
I'm told that the problem did happen before the battery change but got worse later on. I have since removed, cleaned and checked the battery terminals.

The vacuum hoses for the fuel pressure regulator and the MAP sensor come from the same port on the intake. There is a "T" fitting with both hoses. Is there anything about that "T" fitting I could be missing?

That T-fitting is ok unless it's broken or the hoses are loose.

Intake manifold vacuum should be 60 kPa, 450 mmHg or 17.7 inHg at idle. Make sure that your idle is stable before you make a judgement from this measurement. A bad running engine (like one with a miss) will have strange vacuum because you are opening the throttle to make the engine idle correctly. The throttle has to be closed to make a judgement on vacuum with the idle speed around normal.

Compression pressure in a new engine at operating temperature with plugs removed is 178 psi or more. Older engine should be not less than 142 psi with not more than 14 psi difference between cylinders.

Other specs: page EG-1-140 in manual

The battery terminals are not the issue. They are for high current. The connections and wire that you should test is the relatively small one from the positive battery terminal to the fuse box or near the fuse box. This wire can be corroded badly within the insulation and be a poor or intermittent conductor.

The “T” fitting looks good. I also checked it for leaks with carb cleaner. Thanks for the intake vacuum numbers at idle. I went to Harbor Freight Tools tonight to buy a vacuum pump kit made by Pittsburgh, to test the MAP sensor. My luck, the one I bought was bad out of the package. I need to go back and get a new one tomorrow. I’ll check the intake manifold vacuum also.
I’ll try to do a voltage drop test on the wire going to the fuse box.

The weird thing is that I pulled the vacuum hose for the fuel pressure regulator, held my finger on the hose then, plugged the hose back in again. The idle got smooth without doing anything else. A minute or two later, the idle got bad again. Maybe I disturbed the vacuum for the MAP sensor since they are both on the same port. I could be wrong. I need to do more tests. It’s surprising that I would have such bad hesitation under a load without getting any error codes. Thanks again for your help and information. It is greatly appreciated!

Many times, what I do is hang out at a Toyota dealership service department and ask to talk to a mechanic. I always am able to talk to someone who is knowledgeable and give me some ideas on how to solve a problem. If they are an experienced mechanic, they have seen everything.

The weird thing is that I pulled the vacuum hose for the fuel pressure regulator, held my finger on the hose then, plugged the hose back in again. The idle got smooth without doing anything else. A minute or two later, the idle got bad again. Maybe I disturbed the vacuum for the MAP sensor since they are both on the same port. I could be wrong. I need to do more tests. It’s surprising that I would have such bad hesitation under a load without getting any error codes. Thanks again for your help and information. It is greatly appreciated!

If you smell gas in that vacuum line or some gas trickles out, then you have a bad fuel pressure regulator. About $65 at rockauto.

I didn't smell any gas or see any fuel come out of the fuel pressure regulator. I think I have finally narrowed it down now to the area where the problem may be. I hope the results of the MAP sensor test will finally reveal what is wrong. I got a bad vacuum pump tester from Harbor Freight Tools last night and I won't be able to carry out the test until I get a new one. It's is made by Pittsburgh. Maybe I'll opt for the better one made by Mityvac for $12 more. I need something that is reliable especially when troubleshooting something like this with no error codes. Thanks for your help aleekat.

I didn't smell any gas or see any fuel come out of the fuel pressure regulator. I think I have finally narrowed it down now to the area where the problem may be. I hope the results of the MAP sensor test will finally reveal what is wrong. I got a bad vacuum pump tester from Harbor Freight Tools last night and I won't be able to carry out the test until I get a new one. It's is made by Pittsburgh. Maybe I'll opt for the better one made by Mityvac for $12 more. I need something that is reliable especially when troubleshooting something like this with no error codes. Thanks for your help aleekat.

Not out of the regulator, the vacuum hose.

I tested the MAP sensor today and although it is slightly out of spec, I don’t think it’s bad. I have 5 volts reference at the connector. According to the service manual the signal voltage should read 3.96 volts with no vacuum. I read 3.63 volts. Below are the rest of my readings.
Engine Warmed Up
Map signal voltage at idle - 1.5 volts
Vacuum Reading – 33 kpa
23.99 kpa to 37.33 kpa (Service manual specification)

MAP Sensor Bench Test
Reference voltage - 5 volts at connector
Specified Signal voltage with no vacuum – 3.96 volts

Volts Drop
No Vacuum 3.63
13.3 kpa - 100 mmHg 2.79 .86
26.7 kpa - 200 mmHg 2.38 1.27
40.0 kpa - 300 mmHg 1.96 1.67
53.3 kpa - 400 mmHg 1.58 2.07
66.7 kpa - 500 mmHg 1.17 2.48

There was no smell of gas coming from the fuel pressure regulator hose. I went back to AutoZone tonight to rent the fuel pressure test kit and they had one in stock. The next test will be for fuel pressure.
What still confuses me is that the car had no trouble under a load after I advanced the timing but still had a rough idle. Does that mean my fuel pressure is ok as well as my compression?
I also checked the wire coming from the battery to the fuse box and it was good. Thank you.

I would replace the MAP sensor. Do the compression test anyway. It's useful information on the general condition of the engine. Check the fuel pressure and flow rate. It's not likely the problem, but it's difficult to make judgements over the internet. Have you spent some time examining the vacuum hoses? The engine is pretty old to have the original vacuum hoses without at least one bad hose or connection.

I have inspected the vacuum hoses as closely as possible. I even removed a few that I thought were suspect.

Without any error codes I don't have any direction. I'm going around in circles. Before I check fuel pressure, I want to try to use the E1 to TE2 level of diagnostics which I understand is more sensitive. The service manual says I can test drive the car and then, jumper TE1 to E1 to see any additional error codes. Have you done this level of diagnostics before? Thank you.

I checked fuel pressure, and all was good. I decided to go back and check my spark plugs and wires again. I tested them previously with my meter and the resistance was good on all four wires. Today, using a spark tester, I checked the spark on all 4 plugs and they were all good. Then, I noticed at the bottom area of the spark plug connector, there was a very small gray spot on the side. With the spark plug tester on the spark plug and the boot outside the hole, I noticed it sparked to the valve cover from this very tiny gray spot. I checked the other wires and they all had the same little gray spot in the same spot. They were all arcing inside the hole. This not something you can see unless you extend the boot outside the hole. I put in an old set of wires and it fixed the problem.
These are Duralast wires which I purchased from Autozone. They all failed the same way at the same time. I think it’s a defect in the hard-plastic mold. I won’t ever use Duralast again. I saw a set of NGK wires which look pretty good for about $40. Do you have any suggestions about a good set of aftermarket wires comparable to the original wires or should I go to Toyota? Thank you.

NGK wires are top notch. Use them.
http://www.automotiveforums.com/vbulletin/showpost.php?p=7207452&postcount=15

https://www.amazon.com/NGK-TE43-Premium-Spark-Plug/dp/B000IYBESA/ref=sr_1_2?s=automotive&ie=UTF8&qid=1518908976&vehicle=1993-76-1011-269--1-8-5-4853--1-1-1884--5-0&sr=1-2&ymm=1993%3Atoyota%3Acamry

https://www.amazon.com/NGK-Iridium-Spark-Plugs-BKR6EIX-11/dp/B00IZ2ZVOK/ref=sr_1_4?s=automotive&ie=UTF8&qid=1518909092&vehicle=1993-76-1011-269--1-8-5-4853--1-1-1884--5-0&sr=1-4&ymm=1993%3Atoyota%3Acamry

The first thing I did to diagnose this problem was to check the wires, plugs, distributor cap and rotor with my meter and they all checked good. There was never any indication of a misfire while watching the plugs fire with my tester. I ordered a new set of NGK wires, but I am considering removing the Bosch plugs and replacing them with NGK or Denso plugs. I want to run the car for a while to see how it performs long term and then decide.
Another mystery I have not been able to account for is why the misfire went away under a load when I advanced the timing. If the wires are arcing, they should always arc. Also, why did the idle get steady when I removed the vacuum hose from the fuel pressure regulator? There is still a misfire right?
This has been a great learning experience. I enjoyed learning about stoichiometry and how the ECU maintains the 14.7:1 air / fuel ratio based on all the sensors. Unfortunately, this ECU doesn’t report a misfire. The misfire was quite severe under a load and this should have been enough to trigger some kind of a code.
Another observation was that I never got an oxygen sensor error code even when disconnecting the O2 sensor. Probably because it isn’t a heated sensor. It has one wire and from what I understand, the O2 only works after it reaches about 600 to 700 degrees. I see the short-term fuel trim change when accelerating which means the ECU must be using that data. From what I read in the service manual, the ECU can detect open or shorted sensors, but I don’t think it will detect a sensor that is out of specification. The ECU also doesn’t report code 24, IAT sensor. The sensor has voltage going to it and the IAT sensor tested good. I was told that the IAT was not part of OBD1. However, just because it doesn't report the error it may still use the sensor input. Thanks again for you help! I appreciate it.

Thank you for the feedback.