# Confusing Idle Speed Spec for 92 Corolla? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [August 12, 2023, 10:05pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246 "2023-08-12T22:05:13Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 12, 2023, 10:05pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/1 "2023-08-12T22:05:13Z")
92 Toyota Corolla, 4afe engine, manual trans, purchased new in Calif The factory service manual says the idle rpm spec is 700 rpm, and ignition timing should be set at 700 rpm. The emissions sticker on the underside of the hood is very clear, idle rpm is 800 rpm, and timing should be set at the same engine speed , 800 rpm. I’ve always followed the emissions sticker, everything set at 800 rpm, but wondering if that’s actually correct? Does the emissions sticker on the underside of the hood trump the factory service manual? ---
**Author:** ![old\_mopar\_guy](https://avatars.discourse-cdn.com/v4/letter/o/6bbea6/32.png) [@old\_mopar\_guy](https://community.cartalk.com/u/old_mopar_guy)\ **Post date:** [August 12, 2023, 10:41pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/2 "2023-08-12T22:41:47Z")
I’d go with the sticker. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [August 12, 2023, 10:51pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/3 "2023-08-12T22:51:41Z")
The service manual shows 800 rpm for California emission vehicle. ![image](https://global.discourse-cdn.com/cartalk/original/3X/2/c/2c2ec85abb51f2349d3f6f6db1ebd855fac3dcde.png) ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 12, 2023, 11:17pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/4 "2023-08-12T23:17:16Z")
Apparently the 800 rpm spec for Calif didn’t make it into the original factory service manual, or in the same-vintage aftermarket manual. Both say 700 rpm, for either federal or Calif. The only reference I can find for an 800 rpm idle spec is if vehicle is equipped with daytime running lights. But it seems like I’ve been doing it correctly by just following the emissions sticker, thanks for the add’l info. I’ll risk one more question. I wanted to inspect the O2 sensor signal (just one pre-cat o2 sensor on this car) , using an o-scope, but ran into a problem. My plan was to access this signal at the diagnostic connector (check connector as referenced above), a diagram there shows the O2 sensor signal is routed to a pin there; but when probed that location w/the o-scope, got nothing. Zero voltage all the time. Upon further inspection, it appears there is no pin installed in connector location. Is this a common thing w/OBD I vehicles, a pin is shown on the diagnostic connector label, but in fact there isn’t any wire going there? ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [August 13, 2023, 2:29pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/5 "2023-08-13T14:29:11Z")
I would be curious and set it all at 800 rpm and then lower the idle down to 700 rpms and check the timing again, probably very close or the same… ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [August 13, 2023, 6:08pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/6 "2023-08-13T18:08:26Z")
> [@George\_San\_Jose1](#): > > I wanted to inspect the O2 sensor signal (just one pre-cat o2 sensor on this car) , using an o-scope, but ran into a problem. My plan was to access this signal at the diagnostic connector (check connector as referenced above), a diagram there shows the O2 sensor signal is routed to a pin there; but when probed that location w/the o-scope, got nothing. Zero voltage all the time. Upon further inspection, it appears there is no pin installed in connector location. Is this a common thing w/OBD I vehicles, a pin is shown on the diagnostic connector label, but in fact there isn’t any wire going there? No offense, but I don’t know why you’re making it more complicated than it needs to be I would just backprobe the connector directly at the O2 sensor ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 13, 2023, 9:54pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/7 "2023-08-13T21:54:25Z")
> [@db4690](#): > > I would just backprobe the connector directly at the O2 sensor The reason is the o-scope is inside, car is outside, wires in-between. I’d have to figure out a way to clamp the scope probe onto the back-side of the connector. Approaches the limits of my mechanical skills … lol … No need though, I figured out there actually is pin in the diagnostic check connector for the O2 sensor. The pin is positioned much deeper inside the connector than the others I’d already been using. Haven’t had time to look at the o-scope trace yet, discovered another problem, one of the exhaust manifold bolts was so loose it was about to fall out. It’s held on by 5 bolts, 4 were nice & tight, but the one on the far right, not so much. I’m trying to figure out why I’ve had so much grief with the HC emissions on this engine. The allowable limit is 130 ppm, and I consistently get in 90-130 range. It always passes, but just barely, sometimes at 129 … lol … The test report shows an “average” value of 45, but I’m not sure what that’s an average of. All they cars they test? Or all 92 Corolla’s? Or what? And over how many years? Common sense says the report would include a legend explaining what the data means, but it seems Calif’s emissions folks hold their cards close to their vests, job security! … One weird thing I noticed about the O2 sensor wiring, there’s two wires in the car’s wire harness, one is brown, one is black. No other possibility than the brown is the signal and the black is the ground, right? Ooops! Turns out the brown wire is the ground, the black wire is the signal … it’s always something! … lol … ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 16, 2023, 9:14pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/8 "2023-08-16T21:14:35Z")
O-scope results for the O2 sensor: Once the engine reaches normal operating temperature, the O2 sensor output (at idle) varies between 0.2 volts and 0.75 volt in a regular pattern. 1 1/2 seconds going from 0.2 to 0.75, and 1 1/2 second returning to 0.2. Close to a 50% duty cycle over 3 second interval, then it repeats. That all seems spot on, the ECM is clearly monitoring the O2 sensor output, and when it reaches the lean voltage it increases the fuel flow slightly, then when it reaches the rich voltage, it decreases the fuel flow slightly. The only result from this test I found a little surprising, I would have guessed the output would jump from 0.2 to 0.75 volts quickly; but instead it is more like a gradual rise, then a gradual fall. > [@db4690](#): > > I would just backprobe the connector directly at the O2 sensor That connector (O2 sensor to wiring harness) appears to be designed to be extra water-resistant. I’d have to damage the water-proofing in order to do a back- probe. I probed at the check connector instead. > [@davesmopar](#): > > I would be curious and set it all at 800 rpm and then lower the idle down to 700 rpms and check the timing again, probably very close or the same… I tried that, you are right, the ignition timing remains the same. Still a mystery why Calif requires an 800 rpm idle, and everyplace else in the world requires 700 rpm. For the same car, same engine. Wondering if this is why the HC levels have been causing me grief? In other words, if I set the idle at 700 rpm, would the HC levels decrease? (This isn’t possible btw, b/c the idle rpm is tested as part of the process, and must be correct to pass.) If the 800 rpm is the reason, test results of other examples of this engine would prove it. Unfortunately Calif’s emissions folks are holding those test results incognito. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [August 16, 2023, 9:32pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/9 "2023-08-16T21:32:16Z")
> [@George\_San\_Jose1](#): > > Still a mystery why Calif requires an 800 rpm idle, and everyplace else in the world requires 700 rpm One word **California** … I would run a bottle of _ **Marvel Mystery Oil** _ through it and take it in after a 20+ minutes interstate drive at the speed limit or faster… I have also used _ **CRC Guaranteed To Pass Emissions Test Formula** _ on OBD1 vehicles in Tn, don’t know if it would work with y’alls crazy emissions laws though… Do they check the ignition timing also?? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 16, 2023, 9:39pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/10 "2023-08-16T21:39:28Z")
> [@davesmopar](#): > > Do they check the ignition timing also?? Yes. To pass Google says the Calif policy is it must measure within +/- 3 deg of the spec on the under-hood emissions label. There’s a locally produced gasoline additive available here that OBD I & prior car owners seem to think helps when they have emissions test challenges. ---
**Author:** ![old\_mopar\_guy](https://avatars.discourse-cdn.com/v4/letter/o/6bbea6/32.png) [@old\_mopar\_guy](https://community.cartalk.com/u/old_mopar_guy)\ **Post date:** [August 17, 2023, 5:09pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/11 "2023-08-17T17:09:02Z")
They still have timing lights? ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [August 17, 2023, 7:38pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/12 "2023-08-17T19:38:35Z")
> [@George\_San\_Jose1](#): > > The only result from this test I found a little surprising, I would have guessed the output would jump from 0.2 to 0.75 volts quickly; but instead it is more like a gradual rise, then a gradual fall. I think that may be intentional for proper catalyst operation. It intentionally goes rich to get the reaction going and then goes lean reduce emissions. Another method involves injecting clean air in to the exhaust. Does your car have an under the steering wheel diagnostic connector? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 17, 2023, 9:22pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/13 "2023-08-17T21:22:39Z")
> [@TheWonderful90s](#): > > under the steering wheel diagnostic connector? No, Toyota’s OBD I design places the diagnostic connector in the engine compartment. An OBD I diagnostic connector is totally different from an OBD II diagnostic connector, not compatible. ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [August 18, 2023, 2:29am UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/14 "2023-08-18T02:29:41Z")
The 1992 Toyota Camry has two diagnostic connectors. Wondered if yours was similar. The airbag reset uses the under the steering wheel connector that is hanging up there. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [August 18, 2023, 3:02pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/15 "2023-08-18T15:02:18Z")
> [@TheWonderful90s](#): > > The 1992 Toyota Camry has two diagnostic connectors. Wondered if yours was similar. The airbag reset uses the under the steering wheel connector that is hanging up there. I don’t think any of George’s cars have airbags 😸 ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 18, 2023, 9:28pm UTC](https://community.cartalk.com/t/confusing-idle-speed-spec-for-92-corolla/192246/16 "2023-08-18T21:28:43Z")
No airbags.