HARD to start when cold

[johnathan1]

Okay, first problem... My car seems to be really hard to start when cold, but starts fine when warm. Today, (keep in mind it does this all the time, it was just worse today) it was raining, and quite a bit colder than usual, and I swear I didn't think it was going to start, I would crank it for five seconds at a time, and did this probably seven or eight times, before it finally started. When it finally starts, it will idle really low, then jump up to normal RPMs within 1-2 secs. Would a broken ECU temp. sensor cause these kinds of symptoms? I just cleaned my CSI...

Also, when idling, it will miss (I think thats what it's doing, feels to me like it will shake slightly every once in a while) and idle fluctuates slightly every once in a while. It will be at 600 sometimes, and at 900 others, it seems to be perfectly smooth when idling at 900, almost like the car isn't running!

Then, last night, i started to boost slightly, then backed off, and rpms went down, almost died, but then recovered. Also, it is bucking SLIGHTLY under light acceleration... whats the deal?? Thanks!

 

[Nick M]

Before you worry about your air/fuel ratio from sensors, when is the last time you had new factory plugs and wires installed? When the engine is cold, the mixture is richer becuase it is rich is easy to light, and the engine needs heat to fire. If you have a weak spark, it will run rough when cold, or under a load.

That is the starting point. And maybe that will be all you need.

 

[TurboSupra7]

man i have the exact same problem. I mean EXACTLY everything you described happens to my car...I've changed plugs, wires, vacuum hoses, checked for vacuum leaks, new air filter, set TPS. I have another TPS here that I'm going to try and hopefully that will clear up my misfire. As for the hard starting when cold issue, check your cold start injector it could be leaking into the manifold overnight and causing a rich condition making it hard to start.

Edit: Also check the small ground wire that goes onto your coil pack maybe it's loose.

 

[born2drv]

Mine is the same way, it's very rough to start when cold..... when it does start it wants to immediately die out, you need to step on the gas a lot. eventually it just evens itself out and runs smooth.

i replaced nearly EVERYTHING... i mean everything. New battery (relocated to the battery via 0-gauge power wire), 0 gauge ground right to the alternator and starter.... the alternator is new (mr2 100amp), new wires, plugs, the engine was rebuilt recently and a whole bunch of other parts replaced new, but as far as i can remember it always does this. i'm going to replace the cap and rotor, and the 02 sensor next, it was on my list of things to do anyways, i suspect it's the cap/rotor because i can't remember the last time it was replaced and i've owned this car for 11 yrs.

this is my entire list of maintenence/mods:
http://born2drv.com/repair_log.html

i'm keeping very detailed logs this time when everything is replaced so i can eliminate things more easily.

 

[johnathan1]

wow, this sounds like a common problem... It seems like the colder it is, the harder it is to start...it's almost proportional!

I don't think it is the plugs or wires, because the plug wires aren't that old, I tested the plugs and they gave strong spark, it doesn't run rough under load, and it boosts smoothly, very powerful... I don't think it is a boost or vacuum leak, because i checked for those, and I just replaced the lower intercooler hoses. I don't think that it's the CSI, because I cleaned it really good, and put a new high pressure line on it...I don't think the CSSI is at fault, because when the car does start, it immediately goes to around 1200RPMs (cold), and then will gradually go down as the car warms up (which I am thinking is normal...?) My NA used to do these exact same things right before I sold it.

Born2drv: Wow, you have replaced soo much on your car, I can't believe it has trouble! I am also going to replace my o2, i have been getting really bad MPG. I need to start a log too!

Any more ideas anyone?

Also, my thermostat housing looked weird to me, and CRE on here said that it was from a Cressida... OMG! The two lower sensors seem to be missing, but there aren't any connectors for them... Also, my ECU temp sensor is broken, accidently bumped it when putting on the p/s reservoir... I am seriously thinking that is at least part of the problem, with rough idle too...

 

[Nick M]

I have seen a cold start injector leak before, but that usually causes a hot start problem, You need the fuel when cold. If the droplets of fuel do not vaporize, as liquids do not burn, you could have rough starts and idle until warm.

If you live in a cold climate, the cold start injector circuit should be inspected with hard cold starting.

Your ECT sensor may be elctrically short. That means there is no resistance in it. With no resistance, the ECU thinks the car is warm, and will lean out the mixture compared to start up.

 

[jetjock]

Just because you cleaned the CSI doesn't mean it's working. I'd check that it is. If not check the TTS. The cold start system is one of the simplest in the car so the problem shouldn't hard to find. At mimium you'd eliminate it as a possible cause.

 

[johnathan1]

The car doesn't idle roughly when cold, it idles normally, it is just hard to get started... Would that rule out the CSI? And what's the TTS? Also, I just noticed that one of the wires on my 02 sensor has been disconnected (broke off) this whole time, fuck, I hope I didn't blow the hg... I pulled codes and got 21, which is o2 sensor, right? Which o2 sensor can I get? I remember hearing something about buying a mustang o2 sensor from Autozone that would work on the mkiii...which one is it exactly?

 

[jetjock]

A busted O2 and CTS? This engine, as with all modern engines, is dependent on feedback from a network of sensors. It needs a tight electrical system to work right so you need to stay on top of this stuff and fix anything that gets busted.

First the easy part: You can't blow a head gasket with a disconnected O2 sensor. The car will default to slightly rich with it disconnected. Repair the wire or buy a new O2 sensor. I'll leave it to others to suggest where to get one as I don't want to step on any toes.

If the car is hard to start when cold the cause is likely to involve the cold start system (duh). The CSI is an injector that receives fuel from the fuel rail. It sprays when it gets power. Where does it get power? From the starter. In other words it can only spray when the engine is cranking. Stay with me, there's more.

Since we want it to inject when the engine is cold (and only when the engine is cold) something needs to know the temperature of the engine. Coolant temp works best for that so on it's way from the starter to the CSI the power goes through a switch that senses coolant temperature. When the coolant is cold the switch is closed so when you crank the engine the CSI sprays fuel into the intake manifold. When you release the key (after the engine starts) and stop cranking the CSI stops spraying. With me so far?

This switch is called the Thermo Time Switch (TTS). It's the two wire gadget that sticks straight up in the thermostat housing. The "Thermo" part of the name should make sense by now but what about the "Time" part?

Simple. The TTS has a little heater inside that also gets electricity from the starter when the engine is cranking. The little heater is a wire that's wrapped around the contacts that send power on to the CSI. These contacts are bi-metallic. They're two different metals that expand and move apart when heated. It's a thermostat of sorts, a heat sensing switch. So any time the CSI is getting power (only when cranking remember) and spraying fuel, the little heater is heating up the bimetal contacts inside the TTS.

Either one of two things will happen: 1) The car starts and you release the key. This shuts off the CSI because it shuts off the starter. Life is good. 2) The car doesn't start but you keep cranking it. The little heater continues to heat up the contacts and shuts off the CSI anyway after about 8-10 seconds. This prevents the CSI from from flooding the engine. Assuming a no start, on a warm day that could happen in a few seconds. On a cold day that could take all 10 seconds. The colder the coolant the longer it takes to heat up the switch so the longer the CSI sprays (assuming the car doesn't start and you keep cranking).

As a side note it should be obvious that if you crank long enough during a no start to "trip" the TTS and shut off the CSI you need to wait until it cools down because you'll have no cold start injection until it does. So don't bother cranking beyond 15 seconds or so unless it's freezing out or you'll be killing your battery for nothing. And this is if the CSI system is working right to begin with. Put another way, the cold start system gives the engine a limited time to start before it gives up and shuts down. If you get a no start wait a few minutes to let the TTS reset and the battery recover. Otherwise you'll be just pissin' in the wind.

So the TTS works on both temperature and time. Hence the name "Thermo Time Switch". Usually the car starts and the "time" part never happens but it's there to prevent you from filling your manifold with too much fuel. All you need to make the CSI spray is fuel pressure, cranking, and a closed TTS....and good wiring between everything.

Course, if the coolant is hot none of this happens in the first place. The switch is already open from the heat of the coolant and the CSI doesn't spray when cranking. IIRC the rating of the TTS is around 130 degrees. So in a nutshell if the bi-metallic contacts inside it "feel" that temp, either from the coolant or the little heater, power coming from the starter doesn't leave the TTS and cold start injection doesn't occur during cranking.

It's not rocket science. TTSs are used in most cars and tend to have a fairly high failure rate. They're easy to test one you understand how they work.