So, I just bought an 87 Cabrio, with 5spd manual..and I have noticed only 2 small issues. First is, the speedo is about 10mph off. It does have aftermarket Borbet wheels. Is this a common issue? Anyway to correct it? Secondly, when first starting the car, it will idle and sometimes die. It fires right back up, and will go. But once the car warms up, no issues. Also, coincidentally, when the car first starts it runs just fine, but seems like when the car warms up it REALLY COMES alive! The car never misses, or runs badly, but when it warms up it feels MUCH stronger. Is this common?? I appreciate the info!

 

My speedometer is about ten mph off too. As far as starting - never had an issue with warm up.

 

My speedo was off by about 10 miles as well. I sent it in to have it converted from miles to km (I am in Canada) and they put in all new gears. It is still off by 5 or so Km (shows higher than actual speed). Recently, I was in my friends brand new BMW 330i and had my GPS which showed his car off by about 7km/h. When he went to the dealership, they told him that is done on purpose by the manufacturer to keep people from getting speeding tickets. Who knows if that was just a line or not. Call Palo Alto Speedometer in Palo Alto California and ask them what they think.

My car also runs much better when it is warm.

 

You want to figure out if the engine is really running rough when cold or if the idle is just too low or unstable. If the engine runs rough, you may want to look into testing your temp sensor, or other related fuel injection components. You might look into running a can of BG44K through a tankful of gas.

But I would not overlook basic maintenance items. I would change your spark plugs, change the fuel filter, check timing, etc.

 

This may or may not be a potential cause of the speedo error but are the tire diameters anywhere close to the stock size? On all my other vehicles changing to taller/shorter tires has induced a certain degree of error.

 

Thanks for the responses guys! I had definitely considered the bigger wheels having an effect on the speedo, but wouldn't have guessed 10mph. It's comforting to know that other 911's have had the same problem.

As far as cold starts, I can't tell if it actually IS running rough, or if the idle is off. Feels more like the idle is just a big rough. After it warms up, it doesn't have problems, or if it's a warm start there are no issues. But then again, the previous owner did not drive the car very often. That is the reason he sold it. He said maybe 800 miles in the past year or so. So, a part of me is just wondering if it just needs to run through the old gas/get used to being driven again. Never heard of of BG44k before. Is it worth a shot? Is it similar to SeaFoam? Previous owner is a mechanic, so he replaced stuff when it went bad. But if he didn't drive it much, he might not have noticed the rough idle-> running better after warm.

I truly appreciate the info everyone!!!

 

How exactly did you determine the speedo was off?

Ya, I would definitely take the car out on some long drives to see if the problem goes away.

 

I figured out my speedo was off by timing myself between mile markers on the highway. Car felt like it was 10mph off. So, I set the cruise to what i thought was say 75. Timed the mile, which was 47 seconds give or take. Then I did math...at 60mph, you are doing a mile a minute. So, I divided 60 by 75, which gives you .8. Then you multiply that by 60 (as in seconds), which gives you 48 (seconds). So, in the theory was, you figure out the difference it takes to cover a mile...at 75 you cover the mile 20% faster than at 60(i.e. the .8). Then you multiply that by 60, to see how long it SHOULD take you to cover the mile. So 60/75=.8 .8*60=48 seconds. Everytime I did that math that way, the end number was almost exactly my timed speed between mile markers. So, when the car read 75 on the speedo, the time/math ( 55 seconds ) showed it to be 65. I did this several times and different speeds, and the numbers always showed a +10mph. I am going to have a friend pace me to make sure, but I am 95% positive of these results. And to think, I thought I would never use math again after college

 

What size tires are your running? That will determine if it's speedometer = or tire size.

As others have said - I would check all the basic maintenance stuff first before replacing stuff like the cylinder head temp sensor of the the idle control valve. Usually it's the basic stuff with these cars.

 

This is probably a big reason why the engine is running rough. Ever heard of an Italian Tune-up? It is when you take your Ferrari to the mechanic and instead of wrenching on it, the mechanic takes it to the track. The mechanic returns the car to the owner and it runs beautifully. Porsches are not quite the same, but I have heard mechanics advising to have the car taken to a DE or Autocross.

A long drive will also do the trick, but you really have to dip into the throttle and get the RPMs up there. I would run your gas tank nearly out of fuel, fill her up, add a bottle of SeaFoam or equivalent, and take a long, spirited drive.

Yes it is similar, but BG44K is more invasive and expensive. You don't want to put a can in your tank and then let the car sit. You basically want to drive it.

 

So, was over looking the car, and it definitely looks like the plug wires should be changed. which to me, sounds like it could be root of my problems. casually looking at it, the wires twist and wind all over. Is it a pain to change these out? Or does it just look complex? my old mustang is laid out in front of you. thanks again! you all have been great!!!

 

Here are some shots of the car....FYI Anyone know the color name??

 

It's easy to do the wires, just do one at a time. If you are changing the wires might as well do the plugs, rotor, and cap as well.

But remember, one wire at a time. Iceman will tell you what can happen if you mess up the order.

 

As for color, hard to tell from the pics but if it's silver with a purple tint it could be Metallic Rose

 

Looks to me like Nougat Brown Metallic Clearcoat Porsche Code LM8V/L40B

The color code will (should) be under the carpet on the passenger side wheel well in the front trunk - on a sticker.